<s>
Image	O
editing	O
encompasses	O
the	O
processes	O
of	O
altering	O
images	O
,	O
whether	O
they	O
are	O
digital	B-Application
photographs	I-Application
,	O
traditional	O
photo-chemical	O
photographs	O
,	O
or	O
illustrations	O
.	O
</s>
<s>
Graphic	B-Application
software	I-Application
programs	O
,	O
which	O
can	O
be	O
broadly	O
grouped	O
into	O
vector	B-Application
graphics	I-Application
editors	I-Application
,	O
raster	B-Application
graphics	I-Application
editors	I-Application
,	O
and	O
3D	O
modelers	O
,	O
are	O
the	O
primary	O
tools	O
with	O
which	O
a	O
user	O
may	O
manipulate	O
,	O
enhance	O
,	O
and	O
transform	O
images	O
.	O
</s>
<s>
Raster	B-Algorithm
images	I-Algorithm
are	O
stored	O
in	O
a	O
computer	O
in	O
the	O
form	O
of	O
a	O
grid	O
of	O
picture	B-Algorithm
elements	I-Algorithm
,	O
or	O
pixels	B-Algorithm
.	O
</s>
<s>
These	O
pixels	B-Algorithm
contain	O
the	O
image	O
's	O
color	O
and	O
brightness	O
information	O
.	O
</s>
<s>
Image	O
editors	O
can	O
change	O
the	O
pixels	B-Algorithm
to	O
enhance	O
the	O
image	O
in	O
many	O
ways	O
.	O
</s>
<s>
The	O
pixels	B-Algorithm
can	O
be	O
changed	O
as	O
a	O
group	O
,	O
or	O
individually	O
,	O
by	O
the	O
sophisticated	O
algorithms	O
within	O
the	O
image	O
editors	O
.	O
</s>
<s>
This	O
article	O
mostly	O
refers	O
to	O
bitmap	B-Application
graphics	I-Application
editors	I-Application
,	O
which	O
are	O
often	O
used	O
to	O
alter	O
photographs	O
and	O
other	O
raster	B-Algorithm
graphics	I-Algorithm
.	O
</s>
<s>
However	O
,	O
vector	B-Application
graphics	I-Application
software	I-Application
,	O
such	O
as	O
Adobe	B-Language
Illustrator	I-Language
,	O
CorelDRAW	B-Application
,	O
Xara	B-Application
Designer	I-Application
Pro	I-Application
or	O
Inkscape	B-Application
,	O
are	O
used	O
to	O
create	O
and	O
modify	O
vector	O
images	O
,	O
which	O
are	O
stored	O
as	O
descriptions	O
of	O
lines	O
,	O
Bézier	O
curves	B-Algorithm
,	O
and	O
text	O
instead	O
of	O
pixels	B-Algorithm
.	O
</s>
<s>
It	O
is	O
easier	O
to	O
rasterize	O
a	O
vector	O
image	O
than	O
to	O
vectorize	O
a	O
raster	B-Algorithm
image	I-Algorithm
;	O
how	O
to	O
go	O
about	O
vectorizing	O
a	O
raster	B-Algorithm
image	I-Algorithm
is	O
the	O
focus	O
of	O
much	O
research	O
in	O
the	O
field	O
of	O
computer	B-Application
vision	I-Application
.	O
</s>
<s>
They	O
are	O
also	O
scalable	O
,	O
being	O
rasterizable	O
at	O
any	O
resolution	B-Algorithm
.	O
</s>
<s>
Camera	O
or	O
computer	O
image	O
editing	O
programs	O
often	O
offer	O
basic	O
automatic	O
image	O
enhancement	O
features	O
that	O
correct	O
color	O
hue	B-Language
and	O
brightness	O
imbalances	O
as	O
well	O
as	O
other	O
image	O
editing	O
features	O
,	O
such	O
as	O
red	O
eye	O
removal	O
,	O
sharpness	O
adjustments	O
,	O
zoom	B-Algorithm
features	O
and	O
automatic	O
cropping	O
.	O
</s>
<s>
These	O
are	O
called	O
automatic	O
because	O
generally	O
they	O
happen	O
without	O
user	O
interaction	O
or	O
are	O
offered	O
with	O
one	O
click	O
of	O
a	O
button	O
or	O
mouse	O
button	O
or	O
by	O
selecting	B-General_Concept
an	O
option	O
from	O
a	O
menu	O
.	O
</s>
<s>
Many	O
image	O
file	O
formats	O
use	O
data	B-General_Concept
compression	I-General_Concept
to	O
reduce	O
file	O
size	O
and	O
save	O
storage	O
space	O
.	O
</s>
<s>
Both	O
cameras	O
and	O
computer	B-Application
programs	I-Application
allow	O
the	O
user	O
to	O
set	O
the	O
level	O
of	O
compression	O
.	O
</s>
<s>
Some	O
compression	B-General_Concept
algorithms	I-General_Concept
,	O
such	O
as	O
those	O
used	O
in	O
PNG	O
file	O
format	O
,	O
are	O
lossless	B-Algorithm
,	O
which	O
means	O
no	O
information	O
is	O
lost	O
when	O
the	O
file	O
is	O
saved	O
.	O
</s>
<s>
By	O
contrast	O
,	O
the	O
more	O
popular	O
JPEG	O
file	O
format	O
uses	O
a	O
lossy	B-Algorithm
compression	I-Algorithm
algorithm	O
(	O
based	O
on	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
coding	O
)	O
by	O
which	O
the	O
greater	O
the	O
compression	O
,	O
the	O
more	O
information	O
is	O
lost	O
,	O
ultimately	O
reducing	O
image	O
quality	O
or	O
detail	O
that	O
can	O
not	O
be	O
restored	O
.	O
</s>
<s>
One	O
of	O
the	O
prerequisites	O
for	O
many	O
of	O
the	O
applications	O
mentioned	O
below	O
is	O
a	O
method	O
of	O
selecting	B-General_Concept
part(s )	O
of	O
an	O
image	O
,	O
thus	O
applying	O
a	O
change	O
selectively	O
without	O
affecting	O
the	O
entire	O
picture	O
.	O
</s>
<s>
Most	O
graphics	B-Application
programs	I-Application
have	O
several	O
means	O
of	O
accomplishing	O
this	O
,	O
such	O
as	O
:	O
</s>
<s>
a	O
marquee	O
tool	O
for	O
selecting	B-General_Concept
rectangular	O
or	O
other	O
regular	O
polygon-shaped	O
regions	O
,	O
</s>
<s>
as	O
well	O
as	O
more	O
advanced	O
facilities	O
such	O
as	O
edge	B-Algorithm
detection	I-Algorithm
,	O
masking	O
,	O
alpha	B-Algorithm
compositing	I-Algorithm
,	O
and	O
color	O
and	O
channel-based	O
extraction	O
.	O
</s>
<s>
Another	O
feature	O
common	O
to	O
many	O
graphics	B-Application
applications	I-Application
is	O
that	O
of	O
Layers	B-Algorithm
,	O
which	O
are	O
analogous	O
to	O
sheets	O
of	O
transparent	O
acetate	O
(	O
each	O
containing	O
separate	O
elements	O
that	O
make	O
up	O
a	O
combined	O
picture	O
)	O
,	O
stacked	O
on	O
top	O
of	O
each	O
other	O
,	O
each	O
capable	O
of	O
being	O
individually	O
positioned	O
,	O
altered	O
and	O
blended	B-Algorithm
with	O
the	O
layers	B-Algorithm
below	O
,	O
without	O
affecting	O
any	O
of	O
the	O
elements	O
on	O
the	O
other	O
layers	B-Algorithm
.	O
</s>
<s>
Image	O
editors	O
can	O
resize	B-Algorithm
images	I-Algorithm
in	O
a	O
process	O
often	O
called	O
image	B-Algorithm
scaling	I-Algorithm
,	O
making	O
them	O
larger	O
,	O
or	O
smaller	O
.	O
</s>
<s>
High	O
image	B-Algorithm
resolution	I-Algorithm
cameras	O
can	O
produce	O
large	O
images	O
which	O
are	O
often	O
reduced	O
in	O
size	O
for	O
Internet	O
use	O
.	O
</s>
<s>
Image	O
editor	O
programs	O
use	O
a	O
mathematical	O
process	O
called	O
resampling	B-Algorithm
to	O
calculate	O
new	O
pixel	B-Algorithm
values	O
whose	O
spacing	O
is	O
larger	O
or	O
smaller	O
than	O
the	O
original	O
pixel	B-Algorithm
values	O
.	O
</s>
<s>
Images	O
for	O
Internet	O
use	O
are	O
kept	O
small	O
,	O
say	O
640	O
x	O
480	O
pixels	B-Algorithm
which	O
would	O
equal	O
0.3	O
megapixels	B-Algorithm
.	O
</s>
<s>
Cropping	O
creates	O
a	O
new	O
image	O
by	O
selecting	B-General_Concept
a	O
desired	O
rectangular	O
portion	O
from	O
the	O
image	O
being	O
cropped	O
.	O
</s>
<s>
Image	O
cropping	O
does	O
not	O
reduce	O
the	O
resolution	B-Algorithm
of	O
the	O
area	O
cropped	O
.	O
</s>
<s>
Best	O
results	O
are	O
obtained	O
when	O
the	O
original	O
image	O
has	O
a	O
high	B-Algorithm
resolution	I-Algorithm
.	O
</s>
<s>
Image	O
editors	O
have	O
provisions	O
to	O
create	O
an	O
image	B-Algorithm
histogram	I-Algorithm
of	O
the	O
image	O
being	O
edited	O
.	O
</s>
<s>
The	O
histogram	B-Algorithm
plots	O
the	O
number	O
of	O
pixels	B-Algorithm
in	O
the	O
image	O
(	O
vertical	O
axis	O
)	O
with	O
a	O
particular	O
brightness	O
value	O
(	O
horizontal	O
axis	O
)	O
.	O
</s>
<s>
Algorithms	O
in	O
the	O
digital	O
editor	O
allow	O
the	O
user	O
to	O
visually	O
adjust	O
the	O
brightness	O
value	O
of	O
each	O
pixel	B-Algorithm
and	O
to	O
dynamically	O
display	O
the	O
results	O
as	O
adjustments	O
are	O
made	O
.	O
</s>
<s>
Image	O
editors	O
may	O
feature	O
a	O
number	O
of	O
algorithms	O
which	O
can	O
add	O
or	O
remove	O
noise	B-Algorithm
in	O
an	O
image	O
.	O
</s>
<s>
Noise	B-Algorithm
reduction	O
merely	O
estimates	O
the	O
state	O
of	O
the	O
scene	O
without	O
the	O
noise	B-Algorithm
and	O
is	O
not	O
a	O
substitute	O
for	O
obtaining	O
a	O
"	O
cleaner	O
"	O
image	O
.	O
</s>
<s>
Excessive	O
noise	B-Algorithm
reduction	O
leads	O
to	O
a	O
loss	O
of	O
detail	O
,	O
and	O
its	O
application	O
is	O
hence	O
subject	O
to	O
a	O
trade-off	O
between	O
the	O
undesirability	O
of	O
the	O
noise	B-Algorithm
itself	O
and	O
that	O
of	O
the	O
reduction	O
artifacts	O
.	O
</s>
<s>
Noise	B-Algorithm
tends	O
to	O
invade	O
images	O
when	O
pictures	O
are	O
taken	O
in	O
low	O
light	O
settings	O
.	O
</s>
<s>
A	O
new	O
picture	O
can	O
be	O
given	O
an	O
'	O
antiqued	O
 '	O
effect	O
by	O
adding	O
uniform	O
monochrome	O
noise	B-Algorithm
.	O
</s>
<s>
Rotated	O
images	O
usually	O
require	O
cropping	O
afterwards	O
,	O
in	O
order	O
to	O
remove	O
the	O
resulting	O
gaps	O
at	O
the	O
image	B-Algorithm
edges	I-Algorithm
.	O
</s>
<s>
While	O
this	O
might	O
also	O
be	O
useful	O
for	O
special	O
effects	O
,	O
it	O
is	O
the	O
preferred	O
method	O
of	O
correcting	O
the	O
typical	O
perspective	B-Architecture
distortion	O
which	O
results	O
from	O
photographs	O
being	O
taken	O
at	O
an	O
oblique	O
angle	O
to	O
a	O
rectilinear	O
subject	O
.	O
</s>
<s>
Care	O
is	O
needed	O
while	O
performing	O
this	O
task	O
,	O
as	O
the	O
image	O
is	O
reprocessed	O
using	O
interpolation	B-Algorithm
of	O
adjacent	O
pixels	B-Algorithm
,	O
which	O
may	O
reduce	O
overall	O
image	O
definition	O
.	O
</s>
<s>
The	O
effect	O
mimics	O
the	O
use	O
of	O
a	O
perspective	B-Architecture
control	O
lens	O
,	O
which	O
achieves	O
a	O
similar	O
correction	O
in-camera	O
without	O
loss	O
of	O
definition	O
.	O
</s>
<s>
Graphics	B-Application
programs	I-Application
can	O
be	O
used	O
to	O
both	O
sharpen	B-Algorithm
and	O
blur	O
images	O
in	O
a	O
number	O
of	O
ways	O
,	O
such	O
as	O
unsharp	B-Algorithm
masking	I-Algorithm
or	O
deconvolution	O
.	O
</s>
<s>
This	O
can	O
be	O
achieved	O
with	O
a	O
camera	O
by	O
using	O
a	O
large	O
aperture	B-General_Concept
,	O
or	O
in	O
the	O
image	O
editor	O
by	O
making	O
a	O
selection	O
and	O
then	O
blurring	O
it	O
.	O
</s>
<s>
Edge	B-Algorithm
enhancement	I-Algorithm
is	O
an	O
extremely	O
common	O
technique	O
used	O
to	O
make	O
images	O
appear	O
sharper	O
,	O
although	O
purists	O
frown	O
on	O
the	O
result	O
as	O
appearing	O
unnatural	O
.	O
</s>
<s>
This	O
is	O
done	O
by	O
finding	O
the	O
average	O
color	O
of	O
the	O
pixels	B-Algorithm
around	O
each	O
pixel	B-Algorithm
in	O
a	O
specified	O
radius	O
,	O
and	O
then	O
contrasting	O
that	O
pixel	B-Algorithm
from	O
that	O
average	O
color	O
.	O
</s>
<s>
Many	O
graphics	B-Application
applications	I-Application
are	O
capable	O
of	O
merging	O
one	O
or	O
more	O
individual	O
images	O
into	O
a	O
single	O
file	O
.	O
</s>
<s>
When	O
selecting	B-General_Concept
a	O
raster	B-Algorithm
image	I-Algorithm
that	O
is	O
not	O
rectangular	O
,	O
it	O
requires	O
separating	O
the	O
edges	O
from	O
the	O
background	O
,	O
also	O
known	O
as	O
silhouetting	O
.	O
</s>
<s>
Alpha	B-Algorithm
compositing	I-Algorithm
,	O
allows	O
for	O
soft	O
translucent	O
edges	O
when	O
selecting	B-General_Concept
images	O
.	O
</s>
<s>
There	O
are	O
a	O
number	O
of	O
ways	O
to	O
silhouette	O
an	O
image	O
with	O
soft	O
edges	O
,	O
including	O
selecting	B-General_Concept
the	O
image	O
or	O
its	O
background	O
by	O
sampling	O
similar	O
colors	O
,	O
selecting	B-General_Concept
the	O
edges	O
by	O
raster	B-Algorithm
tracing	O
,	O
or	O
converting	O
a	O
clipping	O
path	O
to	O
a	O
raster	B-Algorithm
selection	O
.	O
</s>
<s>
The	O
selection	O
may	O
also	O
be	O
saved	O
in	O
what	O
is	O
known	O
as	O
an	O
alpha	B-Algorithm
channel	I-Algorithm
.	O
</s>
<s>
A	O
popular	O
way	O
to	O
create	O
a	O
composite	O
image	O
is	O
to	O
use	O
transparent	O
layers	B-Algorithm
.	O
</s>
<s>
Performing	O
a	O
merge	O
in	O
this	O
manner	O
preserves	O
all	O
of	O
the	O
pixel	B-Algorithm
data	O
on	O
both	O
layers	B-Algorithm
to	O
more	O
easily	O
enable	O
future	O
changes	O
in	O
the	O
new	O
merged	O
image	O
.	O
</s>
<s>
A	O
more	O
recent	O
tool	O
in	O
digital	O
image	B-Application
editing	I-Application
software	I-Application
is	O
the	O
image	O
slicer	O
.	O
</s>
<s>
Using	O
custom	O
Curves	B-Algorithm
settings	O
in	O
Image	O
editors	O
such	O
as	O
Photoshop	B-Operating_System
,	O
one	O
can	O
mimic	O
the	O
"	O
pseudo-solarisation	O
"	O
effect	O
,	O
better	O
known	O
in	O
photographic	O
circles	O
as	O
the	O
Sabattier-effect	O
.	O
</s>
<s>
The	O
Clone	O
Stamp	O
tool	O
selects	O
and	O
samples	O
an	O
area	O
of	O
your	O
picture	O
and	O
then	O
uses	O
these	O
pixels	B-Algorithm
to	O
paint	O
over	O
any	O
marks	O
.	O
</s>
<s>
The	O
Clone	O
Stamp	O
tool	O
acts	O
like	O
a	O
brush	O
so	O
you	O
can	O
change	O
the	O
size	O
,	O
allowing	O
cloning	O
from	O
just	O
one	O
pixel	B-Algorithm
wide	O
to	O
hundreds	O
.	O
</s>
<s>
In	O
Photoshop	B-Operating_System
this	O
tool	O
is	O
called	O
Clone	O
Stamp	O
,	O
but	O
it	O
may	O
also	O
be	O
called	O
a	O
Rubber	O
Stamp	O
tool	O
.	O
</s>
<s>
In	O
addition	O
,	O
grayscale	O
images	O
of	O
8	O
bits	O
or	O
less	O
can	O
be	O
created	O
,	O
usually	O
via	O
conversion	O
and	O
down-sampling	B-Algorithm
from	O
a	O
full-color	O
image	O
.	O
</s>
<s>
Recent	O
advances	O
have	O
allowed	O
more	O
intelligent	O
exposure	O
correction	O
whereby	O
only	O
pixels	B-Algorithm
below	O
a	O
particular	O
luminosity	O
threshold	O
are	O
brightened	O
,	O
thereby	O
brightening	O
underexposed	O
shadows	O
without	O
affecting	O
the	O
rest	O
of	O
the	O
image	O
.	O
</s>
<s>
GIMP	B-Application
applies	O
the	O
following	O
formula	O
:	O
</s>
<s>
In	O
some	O
image	B-Application
editing	I-Application
software	I-Application
,	O
this	O
is	O
called	O
"	O
curves	B-Algorithm
"	O
,	O
usually	O
,	O
a	O
tool	O
found	O
in	O
the	O
color	O
menu	O
,	O
and	O
no	O
reference	O
to	O
"	O
gamma	O
"	O
is	O
used	O
anywhere	O
in	O
the	O
program	O
or	O
the	O
program	O
documentation	O
.	O
</s>
<s>
Strictly	O
speaking	O
,	O
the	O
curves	B-Algorithm
tool	O
usually	O
does	O
more	O
than	O
simple	O
gamma	O
correction	O
,	O
since	O
one	O
can	O
construct	O
complex	O
curves	B-Algorithm
with	O
multiple	O
inflection	O
points	O
,	O
but	O
when	O
no	O
dedicated	O
gamma	O
correction	O
tool	O
is	O
provided	O
,	O
it	O
can	O
achieve	O
the	O
same	O
effect	O
.	O
</s>
<s>
Colors	O
can	O
be	O
faded	O
in	O
and	O
out	O
,	O
and	O
tones	O
can	O
be	O
changed	O
using	O
curves	B-Algorithm
or	O
other	O
tools	O
.	O
</s>
<s>
The	O
color	B-Algorithm
balance	I-Algorithm
can	O
be	O
improved	O
,	O
which	O
is	O
important	O
if	O
the	O
picture	O
was	O
shot	O
indoors	O
with	O
daylight	O
film	O
,	O
or	O
shot	O
on	O
a	O
camera	O
with	O
the	O
white	B-Algorithm
balance	I-Algorithm
incorrectly	O
set	O
.	O
</s>
<s>
In	O
addition	O
,	O
more	O
complicated	O
procedures	O
such	O
as	O
the	O
mixing	O
of	O
color	O
channels	O
are	O
possible	O
using	O
more	O
advanced	O
graphics	B-Application
editors	I-Application
.	O
</s>
<s>
Advanced	O
Dynamic	O
Blending	O
is	O
a	O
concept	O
introduced	O
by	O
photographer	O
Elia	O
Locardi	O
in	O
his	O
blog	O
Blame	B-Algorithm
The	I-Algorithm
Monkey	I-Algorithm
to	O
describe	O
the	O
photographic	O
process	O
of	O
capturing	O
multiple	O
bracketed	O
exposures	O
of	O
a	O
land	O
or	O
cityscape	O
over	O
a	O
specific	O
span	O
of	O
time	O
in	O
a	O
changing	O
natural	O
or	O
artificial	O
lighting	O
environment	O
.	O
</s>
<s>
Once	O
captured	O
,	O
the	O
exposure	O
brackets	O
are	O
manually	O
blended	B-Algorithm
together	O
into	O
a	O
single	O
High	O
Dynamic	O
Range	O
image	O
using	O
post-processing	O
software	O
.	O
</s>
<s>
Controlling	O
the	O
print	O
size	O
and	O
quality	O
of	O
digital	O
images	O
requires	O
an	O
understanding	O
of	O
the	O
pixels-per-inch	B-Algorithm
(	O
ppi	O
)	O
variable	O
that	O
is	O
stored	O
in	O
the	O
image	O
file	O
and	O
sometimes	O
used	O
to	O
control	O
the	O
size	O
of	O
the	O
printed	O
image	O
.	O
</s>
<s>
Within	O
Adobe	B-Operating_System
Photoshop	I-Operating_System
's	O
Image	B-Algorithm
Size	I-Algorithm
dialog	O
,	O
the	O
image	O
editor	O
allows	O
the	O
user	O
to	O
manipulate	O
both	O
pixel	B-Algorithm
dimensions	O
and	O
the	O
size	O
of	O
the	O
image	O
on	O
the	O
printed	O
document	O
.	O
</s>
<s>
Pixels	B-Algorithm
per	I-Algorithm
inch	I-Algorithm
of	O
the	O
image	O
,	O
pixel	B-Algorithm
per	O
inch	O
of	O
the	O
computer	O
monitor	O
,	O
and	O
dots	O
per	O
inch	O
on	O
the	O
printed	O
document	O
are	O
related	O
,	O
but	O
in	O
use	O
are	O
very	O
different	O
.	O
</s>
<s>
The	O
Image	B-Algorithm
Size	I-Algorithm
dialog	O
can	O
be	O
used	O
as	O
an	O
image	O
calculator	O
of	O
sorts	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
1600	O
×	O
1200	O
image	O
with	O
a	O
resolution	B-Algorithm
of	O
200ppi	O
will	O
produce	O
a	O
printed	O
image	O
of	O
8	O
×	O
6inches	O
.	O
</s>
<s>
Change	O
the	O
resolution	B-Algorithm
to	O
800ppi	O
,	O
and	O
the	O
same	O
image	O
now	O
prints	O
out	O
at	O
2	O
×	O
1.5inches	O
.	O
</s>
<s>
All	O
three	O
printed	O
images	O
contain	O
the	O
same	O
data	O
(	O
1600	O
×	O
1200	O
pixels	B-Algorithm
)	O
,	O
but	O
the	O
pixels	B-Algorithm
are	O
closer	O
together	O
on	O
the	O
smaller	O
prints	O
,	O
so	O
the	O
smaller	O
images	O
will	O
potentially	O
look	O
sharp	O
when	O
the	O
larger	O
ones	O
do	O
not	O
.	O
</s>
