<s>
right|thumb|upright	O
=	O
1|The	O
smiley	O
face	O
in	O
the	O
top	O
left	O
corner	O
is	O
a	O
raster	B-Algorithm
image	I-Algorithm
.	O
</s>
<s>
When	O
enlarged	O
,	O
individual	O
pixels	B-Algorithm
appear	O
as	O
squares	O
.	O
</s>
<s>
Enlarging	O
further	O
,	O
each	O
pixel	B-Algorithm
can	O
be	O
analyzed	O
,	O
with	O
their	O
colors	O
constructed	O
through	O
combination	O
of	O
the	O
values	O
for	O
red	O
,	O
green	O
and	O
blue	O
.	O
</s>
<s>
In	O
computer	O
graphics	O
and	O
digital	B-Application
photography	I-Application
,	O
a	O
raster	B-Algorithm
graphic	I-Algorithm
represents	O
a	O
two-dimensional	O
picture	O
as	O
a	O
rectangular	B-Architecture
matrix	I-Architecture
or	O
grid	O
of	O
square	O
pixels	B-Algorithm
,	O
viewable	O
via	O
a	O
computer	B-Device
display	I-Device
,	O
paper	O
,	O
or	O
other	O
display	O
medium	O
.	O
</s>
<s>
A	O
raster	O
is	O
technically	O
characterized	O
by	O
the	O
width	O
and	O
height	O
of	O
the	O
image	O
in	O
pixels	B-Algorithm
and	O
by	O
the	O
number	O
of	O
bits	O
per	O
pixel	B-Algorithm
.	O
</s>
<s>
Raster	B-Algorithm
images	I-Algorithm
are	O
stored	O
in	O
image	O
files	O
with	O
varying	O
dissemination	O
,	O
production	B-Application
,	O
generation	O
,	O
and	O
acquisition	B-Application
formats	I-Application
.	O
</s>
<s>
The	O
printing	O
and	O
prepress	O
industries	O
know	O
raster	B-Algorithm
graphics	I-Algorithm
as	O
contones	B-Algorithm
(	O
from	O
continuous	O
tones	O
)	O
.	O
</s>
<s>
Many	O
raster	O
manipulations	O
map	O
directly	O
onto	O
the	O
mathematical	O
formalisms	O
of	O
linear	B-Language
algebra	I-Language
,	O
where	O
mathematical	O
objects	O
of	O
matrix	B-Architecture
structure	O
are	O
of	O
central	O
concern	O
.	O
</s>
<s>
It	O
originates	O
from	O
the	O
raster	O
scan	O
of	O
cathode	B-Device
ray	I-Device
tube	I-Device
(	O
CRT	O
)	O
video	O
monitors	O
,	O
which	O
paint	O
the	O
image	O
line	O
by	O
line	O
by	O
magnetically	O
or	O
electrostatically	O
steering	O
a	O
focused	O
electron	O
beam	O
.	O
</s>
<s>
By	O
association	O
,	O
it	O
can	O
also	O
refer	O
to	O
a	O
rectangular	O
grid	O
of	O
pixels	B-Algorithm
.	O
</s>
<s>
The	O
fundamental	O
strategy	O
underlying	O
the	O
raster	O
data	O
model	O
is	O
the	O
tessellation	B-Algorithm
of	O
a	O
plane	O
,	O
into	O
a	O
two-dimensional	O
array	O
of	O
squares	O
,	O
each	O
called	O
a	O
cell	O
or	O
pixel	B-Algorithm
(	O
from	O
"	O
picture	B-Algorithm
element	I-Algorithm
"	O
)	O
.	O
</s>
<s>
In	O
digital	B-Application
photography	I-Application
,	O
the	O
plane	O
is	O
the	O
visual	O
field	O
as	O
projected	O
onto	O
the	O
image	B-Algorithm
sensor	I-Algorithm
;	O
in	O
computer	O
art	O
,	O
the	O
plane	O
is	O
a	O
virtual	O
canvas	O
;	O
in	O
geographic	B-Application
information	I-Application
systems	I-Application
,	O
the	O
plane	O
is	O
a	O
projection	B-Application
of	O
the	O
Earth	O
's	O
surface	O
.	O
</s>
<s>
The	O
size	O
of	O
each	O
square	O
pixel	B-Algorithm
,	O
known	O
as	O
the	O
resolution	O
or	O
support	O
,	O
is	O
constant	O
across	O
the	O
grid	O
.	O
</s>
<s>
A	O
single	O
numeric	O
value	O
is	O
then	O
stored	O
for	O
each	O
pixel	B-Algorithm
.	O
</s>
<s>
Each	O
raster	O
grid	O
has	O
a	O
specified	O
pixel	B-Algorithm
format	O
,	O
the	O
data	O
type	O
for	O
each	O
number	O
.	O
</s>
<s>
Common	O
pixel	B-Algorithm
formats	O
are	O
binary	B-Algorithm
,	O
gray-scale	O
,	O
palettized	B-Data_Structure
,	O
and	O
full-color	O
,	O
where	O
color	O
depth	O
determines	O
the	O
fidelity	O
of	O
the	O
colors	O
represented	O
,	O
and	O
color	B-Algorithm
space	I-Algorithm
determines	O
the	O
range	O
of	O
color	O
coverage	O
(	O
which	O
is	O
often	O
less	O
than	O
the	O
full	O
range	O
of	O
human	O
color	O
vision	O
)	O
.	O
</s>
<s>
Most	O
modern	O
color	O
raster	B-Algorithm
formats	I-Algorithm
represent	O
color	O
using	O
24bits	O
(	O
over	O
16million	O
distinct	O
colors	O
)	O
,	O
with	O
8bits	O
(	O
values	O
0	O
–	O
255	O
)	O
for	O
each	O
color	B-Algorithm
channel	I-Algorithm
(	O
red	O
,	O
green	O
,	O
and	O
blue	O
)	O
.	O
</s>
<s>
The	O
digital	O
sensors	O
used	O
for	O
remote	B-Application
sensing	I-Application
and	O
astronomy	O
are	O
often	O
able	O
to	O
detect	O
and	O
store	O
wavelengths	O
beyond	O
the	O
visible	O
spectrum	O
;	O
the	O
large	O
CCD	B-Algorithm
bitmapped	B-Algorithm
sensor	O
at	O
the	O
Vera	O
C	O
.	O
Rubin	O
Observatory	O
captures	O
3.2gigapixels	O
in	O
a	O
single	O
image	O
(	O
6.4GB	O
raw	O
)	O
,	O
over	O
six	O
color	B-Algorithm
channels	I-Algorithm
which	O
exceed	O
the	O
spectral	O
range	O
of	O
human	O
color	O
vision	O
.	O
</s>
<s>
Most	O
computer	O
images	O
are	O
stored	O
in	O
raster	B-Algorithm
graphics	I-Algorithm
formats	O
or	O
compressed	O
variations	O
,	O
including	O
GIF	O
,	O
JPEG	O
,	O
and	O
PNG	O
,	O
which	O
are	O
popular	O
on	O
the	O
World	O
Wide	O
Web	O
.	O
</s>
<s>
A	O
raster	O
data	O
structure	O
is	O
based	O
on	O
a	O
(	O
usually	O
rectangular	O
,	O
square-based	O
)	O
tessellation	B-Algorithm
of	O
the	O
2D	O
plane	O
into	O
cells	O
,	O
each	O
containing	O
a	O
single	O
value	O
.	O
</s>
<s>
In	O
the	O
example	O
at	O
right	O
,	O
the	O
cells	O
of	O
tessellation	B-Algorithm
A	O
are	O
overlaid	O
on	O
the	O
point	O
pattern	O
B	O
resulting	O
in	O
an	O
array	O
C	O
of	O
quadrant	O
counts	O
representing	O
the	O
number	O
of	O
points	O
in	O
each	O
cell	O
.	O
</s>
<s>
For	O
purposes	O
of	O
visualization	O
a	O
lookup	B-Data_Structure
table	I-Data_Structure
has	O
been	O
used	O
to	O
color	O
each	O
of	O
the	O
cells	O
in	O
an	O
image	O
D	O
.	O
Here	O
are	O
the	O
numbers	O
as	O
a	O
serial	O
row-major	O
array	O
:	O
</s>
<s>
To	O
reconstruct	O
the	O
two-dimensional	O
grid	O
,	O
the	O
file	O
must	O
include	O
a	O
header	O
section	O
at	O
the	O
beginning	O
that	O
contains	O
at	O
least	O
the	O
number	O
of	O
columns	O
,	O
and	O
the	O
pixel	B-Algorithm
datatype	O
(	O
especially	O
the	O
number	O
of	O
bits	O
or	O
bytes	O
per	O
value	O
)	O
so	O
the	O
reader	O
knows	O
where	O
each	O
value	O
ends	O
to	O
start	O
reading	O
the	O
next	O
one	O
.	O
</s>
<s>
Headers	O
may	O
also	O
include	O
the	O
number	O
of	O
rows	O
,	O
georeferencing	B-General_Concept
parameters	O
for	O
geographic	O
data	O
,	O
or	O
other	O
metadata	O
tags	O
,	O
such	O
as	O
those	O
specified	O
in	O
the	O
Exif	O
standard	O
.	O
</s>
<s>
High-resolution	O
raster	O
grids	O
contain	O
a	O
large	O
number	O
of	O
pixels	B-Algorithm
,	O
and	O
thus	O
consume	O
a	O
large	O
amount	O
of	O
memory	O
.	O
</s>
<s>
The	O
most	O
common	O
strategy	O
is	O
to	O
look	O
for	O
patterns	O
or	O
trends	O
in	O
the	O
pixel	B-Algorithm
values	O
,	O
then	O
store	O
a	O
parameterized	O
form	O
of	O
the	O
pattern	O
instead	O
of	O
the	O
original	O
data	O
.	O
</s>
<s>
Common	O
raster	O
compression	O
algorithms	O
include	O
run-length	B-Algorithm
encoding	I-Algorithm
(	O
RLE	O
)	O
,	O
JPEG	O
,	O
LZ	B-Algorithm
(	O
the	O
basis	O
for	O
PNG	O
and	O
ZIP	B-General_Concept
)	O
,	O
LZW	B-Algorithm
(	O
the	O
basis	O
for	O
GIF	O
)	O
,	O
and	O
others	O
.	O
</s>
<s>
For	O
example	O
,	O
Run	B-Algorithm
length	I-Algorithm
encoding	I-Algorithm
looks	O
for	O
repeated	O
values	O
in	O
the	O
array	O
,	O
and	O
replaces	O
them	O
with	O
the	O
value	O
and	O
the	O
number	O
of	O
times	O
it	O
appears	O
.	O
</s>
<s>
This	O
technique	O
is	O
very	O
efficient	O
when	O
there	O
are	O
large	O
areas	O
of	O
identical	O
values	O
,	O
such	O
as	O
a	O
line	O
drawing	O
,	O
but	O
in	O
a	O
photograph	O
where	O
pixels	B-Algorithm
are	O
usually	O
slightly	O
different	O
from	O
their	O
neighbors	O
,	O
the	O
RLE	O
file	O
would	O
be	O
up	O
to	O
twice	O
the	O
size	O
of	O
the	O
original	O
.	O
</s>
<s>
Some	O
compression	O
algorithms	O
,	O
such	O
as	O
RLE	O
and	O
LZW	B-Algorithm
,	O
are	O
lossless	O
,	O
where	O
the	O
original	O
pixel	B-Algorithm
values	O
can	O
be	O
perfectly	O
regenerated	O
from	O
the	O
compressed	O
data	O
.	O
</s>
<s>
Other	O
algorithms	O
,	O
such	O
as	O
JPEG	O
,	O
are	O
lossy	O
,	O
because	O
the	O
parameterized	O
patterns	O
are	O
only	O
an	O
approximation	O
of	O
the	O
original	O
pixel	B-Algorithm
values	O
,	O
so	O
the	O
latter	O
can	O
only	O
be	O
estimated	O
from	O
the	O
compressed	O
data	O
.	O
</s>
<s>
Vector	O
images	O
(	O
line	O
work	O
)	O
can	O
be	O
rasterized	O
(	O
converted	O
into	O
pixels	B-Algorithm
)	O
,	O
and	O
raster	B-Algorithm
images	I-Algorithm
vectorized	O
(	O
raster	B-Algorithm
images	I-Algorithm
converted	O
into	O
vector	O
graphics	O
)	O
,	O
by	O
software	O
.	O
</s>
<s>
In	O
both	O
cases	O
some	O
information	O
is	O
lost	O
,	O
although	O
certain	O
vectorization	O
operations	O
can	O
recreate	O
salient	O
information	O
,	O
as	O
in	O
the	O
case	O
of	O
optical	B-Application
character	I-Application
recognition	I-Application
.	O
</s>
<s>
Early	O
mechanical	B-Architecture
televisions	I-Architecture
developed	O
in	O
the	O
1920s	O
employed	O
rasterization	O
principles	O
.	O
</s>
<s>
Electronic	O
television	O
based	O
on	O
cathode-ray	B-Device
tube	I-Device
displays	O
are	O
raster	O
scanned	O
with	O
horizontal	O
rasters	O
painted	O
left	O
to	O
right	O
,	O
and	O
the	O
raster	O
lines	O
painted	O
top	O
to	O
bottom	O
.	O
</s>
<s>
Each	O
on-screen	O
pixel	B-Algorithm
directly	O
corresponds	O
to	O
a	O
small	O
number	O
of	O
bits	O
in	O
memory	O
.	O
</s>
<s>
The	O
screen	O
is	O
refreshed	O
simply	O
by	O
scanning	O
through	O
pixels	B-Algorithm
and	O
coloring	O
them	O
according	O
to	O
each	O
set	O
of	O
bits	O
.	O
</s>
<s>
The	O
refresh	O
procedure	O
,	O
being	O
speed	O
critical	O
,	O
is	O
often	O
implemented	O
by	O
dedicated	O
circuitry	O
,	O
often	O
as	O
a	O
part	O
of	O
a	O
graphics	B-Architecture
processing	I-Architecture
unit	I-Architecture
.	O
</s>
<s>
The	O
bits	O
of	O
data	O
stored	O
in	O
this	O
block	O
of	O
memory	O
are	O
related	O
to	O
the	O
eventual	O
pattern	O
of	O
pixels	B-Algorithm
that	O
will	O
be	O
used	O
to	O
construct	O
an	O
image	O
on	O
the	O
display	O
.	O
</s>
<s>
During	O
the	O
1970s	O
and	O
1980s	O
,	O
pen	B-Operating_System
plotters	I-Operating_System
,	O
using	O
Vector	O
graphics	O
,	O
were	O
common	O
for	O
creating	O
precise	O
drawings	O
,	O
especially	O
on	O
large	O
format	O
paper	O
.	O
</s>
<s>
When	O
the	O
source	O
information	O
is	O
vector	O
,	O
rendering	O
specifications	O
and	O
software	O
such	O
as	O
PostScript	B-Language
are	O
used	O
to	O
create	O
the	O
raster	B-Algorithm
image	I-Algorithm
.	O
</s>
<s>
Three-dimensional	O
voxel	B-Algorithm
raster	B-Algorithm
graphics	I-Algorithm
are	O
employed	O
in	O
video	O
games	O
and	O
are	O
also	O
used	O
in	O
medical	O
imaging	O
such	O
as	O
MRI	O
scanners	O
.	O
</s>
<s>
Geographic	O
phenomena	O
are	O
commonly	O
represented	O
in	O
a	O
raster	B-Algorithm
format	I-Algorithm
in	O
GIS	B-Application
.	O
</s>
<s>
The	O
raster	O
grid	O
is	O
georeferenced	B-General_Concept
,	O
so	O
that	O
each	O
pixel	B-Algorithm
(	O
commonly	O
called	O
a	O
cell	O
in	O
GIS	B-Application
because	O
the	O
"	O
picture	O
"	O
part	O
of	O
"	O
pixel	B-Algorithm
"	O
is	O
not	O
relevant	O
)	O
represents	O
a	O
square	O
region	O
of	O
geographic	O
space	O
.	O
</s>
<s>
Raster	B-Algorithm
graphics	I-Algorithm
are	O
resolution	O
dependent	O
,	O
meaning	O
they	O
cannot	O
scale	O
up	O
to	O
an	O
arbitrary	O
resolution	O
without	O
loss	B-Algorithm
of	I-Algorithm
apparent	I-Algorithm
quality	I-Algorithm
.	O
</s>
<s>
Raster	B-Algorithm
graphics	I-Algorithm
deal	O
more	O
practically	O
than	O
vector	O
graphics	O
with	O
photographs	O
and	O
photo-realistic	O
images	O
,	O
while	O
vector	O
graphics	O
often	O
serve	O
better	O
for	O
typesetting	O
or	O
for	O
graphic	O
design	O
.	O
</s>
<s>
Modern	O
computer-monitors	O
typically	O
display	O
about	O
72	O
to	O
130	O
pixels	B-Algorithm
per	I-Algorithm
inch	I-Algorithm
(	O
PPI	O
)	O
,	O
and	O
some	O
modern	O
consumer	O
printers	O
can	O
resolve	O
2400	O
dots	O
per	O
inch	O
(	O
DPI	O
)	O
or	O
more	O
;	O
determining	O
the	O
most	O
appropriate	O
image	O
resolution	O
for	O
a	O
given	O
printer-resolution	O
can	O
pose	O
difficulties	O
,	O
since	O
printed	O
output	O
may	O
have	O
a	O
greater	O
level	O
of	O
detail	O
than	O
a	O
viewer	O
can	O
discern	O
on	O
a	O
monitor	O
.	O
</s>
<s>
Because	O
,	O
through	O
the	O
dithering	O
process	O
,	O
the	O
printer	O
builds	O
a	O
single	O
image	O
pixel	B-Algorithm
out	O
of	O
several	O
printer	O
dots	O
to	O
increase	O
color	O
depth	O
,	O
the	O
printer	O
's	O
DPI	O
setting	O
must	O
be	O
set	O
far	O
higher	O
than	O
the	O
desired	O
PPI	O
to	O
ensure	O
sufficient	O
color	O
depth	O
without	O
sacrificing	O
image	O
resolution	O
.	O
</s>
<s>
Raster-based	O
image	O
editors	O
,	O
such	O
as	O
PaintShop	B-Application
Pro	I-Application
,	O
Corel	B-Operating_System
Painter	I-Operating_System
,	O
Adobe	B-Operating_System
Photoshop	I-Operating_System
,	O
Paint.NET	B-Language
,	O
Microsoft	B-Application
Paint	I-Application
,	O
and	O
GIMP	B-Application
,	O
revolve	O
around	O
editing	O
pixels	B-Algorithm
,	O
unlike	O
vector-based	O
image	O
editors	O
,	O
such	O
as	O
Xfig	B-Application
,	O
CorelDRAW	B-Application
,	O
Adobe	B-Language
Illustrator	I-Language
,	O
or	O
Inkscape	B-Application
,	O
which	O
revolve	O
around	O
editing	O
lines	O
and	O
shapes	O
(	O
vectors	O
)	O
.	O
</s>
<s>
When	O
an	O
image	O
is	O
rendered	O
in	O
a	O
raster-based	O
image	O
editor	O
,	O
the	O
image	O
is	O
composed	O
of	O
millions	O
of	O
pixels	B-Algorithm
.	O
</s>
<s>
At	O
its	O
core	O
,	O
a	O
raster	B-Application
image	I-Application
editor	I-Application
works	O
by	O
manipulating	O
each	O
individual	O
pixel	B-Algorithm
.	O
</s>
<s>
Most	O
pixel-based	O
image	O
editors	O
work	O
using	O
the	O
RGB	O
color	O
model	O
,	O
but	O
some	O
also	O
allow	O
the	O
use	O
of	O
other	O
color	O
models	O
such	O
as	O
the	O
CMYK	O
color	O
model	O
.	O
</s>
