<s>
In	O
computing	O
,	O
indexed	B-Data_Structure
color	I-Data_Structure
is	O
a	O
technique	O
to	O
manage	O
digital	B-Algorithm
images	I-Algorithm
 '	O
colors	O
in	O
a	O
limited	O
fashion	O
,	O
in	O
order	O
to	O
save	O
computer	O
memory	B-General_Concept
and	O
file	B-Device
storage	I-Device
,	O
while	O
speeding	O
up	O
display	O
refresh	O
and	O
file	O
transfers	O
.	O
</s>
<s>
It	O
is	O
a	O
form	O
of	O
vector	O
quantization	O
compression	B-General_Concept
.	O
</s>
<s>
When	O
an	O
image	O
is	O
encoded	B-Algorithm
in	O
this	O
way	O
,	O
color	O
information	O
is	O
not	O
directly	O
carried	O
by	O
the	O
image	O
pixel	B-Algorithm
data	O
,	O
but	O
is	O
stored	O
in	O
a	O
separate	O
piece	O
of	O
data	O
called	O
a	O
color	B-Data_Structure
lookup	I-Data_Structure
table	I-Data_Structure
(	O
CLUT	B-Data_Structure
)	O
or	O
palette	B-Data_Structure
:	O
an	O
array	O
of	O
color	O
specifications	O
.	O
</s>
<s>
Each	O
image	O
pixel	B-Algorithm
does	O
not	O
contain	O
the	O
full	O
specification	O
of	O
its	O
color	O
,	O
but	O
only	O
its	O
index	O
into	O
the	O
palette	B-Data_Structure
.	O
</s>
<s>
Early	O
graphics	O
display	O
systems	O
that	O
used	O
8-bit	O
indexed	B-Data_Structure
color	I-Data_Structure
with	O
frame	B-Algorithm
buffers	I-Algorithm
and	O
color	B-Data_Structure
lookup	I-Data_Structure
tables	I-Data_Structure
include	O
Shoup	O
's	O
SuperPaint	B-Application
(	O
1973	O
)	O
and	O
the	O
video	O
frame	B-Algorithm
buffer	I-Algorithm
described	O
in	O
1975	O
by	O
Kajiya	O
,	O
Sutherland	O
,	O
and	O
Cheadle	O
.	O
</s>
<s>
These	O
supported	O
a	O
palette	B-Data_Structure
of	O
256	O
RGB	O
colors	O
.	O
</s>
<s>
SuperPaint	B-Application
used	O
a	O
shift-register	B-General_Concept
frame	B-Algorithm
buffer	I-Algorithm
,	O
while	O
the	O
Kajiya	O
et	O
al	O
.	O
</s>
<s>
system	O
used	O
a	O
random-access	B-Architecture
frame	B-Algorithm
buffer	I-Algorithm
.	O
</s>
<s>
A	O
few	O
earlier	O
systems	O
used	O
3-bit	O
color	O
,	O
but	O
typically	O
treated	O
the	O
bits	O
as	O
independent	O
red	O
,	O
green	O
,	O
and	O
blue	O
on/off	O
bits	O
rather	O
than	O
jointly	O
as	O
an	O
index	O
into	O
a	O
CLUT	B-Data_Structure
.	O
</s>
<s>
per	O
byte	B-Application
if	O
using	O
4	O
colors	O
)	O
.	O
</s>
<s>
bitmap	B-Algorithm
or	O
bilevel	O
image	O
)	O
and	O
not	O
an	O
indexed	B-Data_Structure
color	I-Data_Structure
image	O
.	O
</s>
<s>
hardware	B-Architecture
.	O
</s>
<s>
Indexed	B-Data_Structure
color	I-Data_Structure
images	O
with	O
palette	B-Data_Structure
sizes	O
beyond	O
256	O
entries	O
are	O
rare	O
.	O
</s>
<s>
practical	O
limit	O
is	O
around	O
12-bit	O
per	O
pixel	B-Algorithm
,	O
4,096	O
different	O
indices	O
.	O
</s>
<s>
color	B-Algorithm
quantization	I-Algorithm
.	O
</s>
<s>
How	O
the	O
colors	O
are	O
encoded	B-Algorithm
within	O
the	O
color	O
palette	B-Data_Structure
map	O
of	O
a	O
given	O
indexed	B-Data_Structure
color	I-Data_Structure
image	O
depends	O
on	O
the	O
target	O
platform	O
.	O
</s>
<s>
Many	O
early	O
personal	B-Device
and	O
home	O
computers	O
had	O
very	O
limited	O
hardware	B-Architecture
palettes	B-Data_Structure
that	O
could	O
produce	O
a	O
very	O
small	O
set	O
of	O
colors	O
.	O
</s>
<s>
In	O
these	O
cases	O
,	O
each	O
pixel	B-Algorithm
's	O
value	O
mapped	O
directly	O
onto	O
one	O
of	O
these	O
colors	O
.	O
</s>
<s>
Well-known	O
examples	O
include	O
the	O
Apple	O
II	O
,	O
Commodore	O
64	O
and	O
IBM	O
PC	O
CGA	B-Device
,	O
all	O
of	O
which	O
included	O
hardware	B-Architecture
that	O
could	O
produce	O
a	O
fixed	O
set	O
of	O
16	O
colors	O
.	O
</s>
<s>
In	O
these	O
cases	O
,	O
an	O
image	O
can	O
encode	O
each	O
pixel	B-Algorithm
with	O
4-bits	O
,	O
directly	O
selecting	O
the	O
color	O
to	O
use	O
.	O
</s>
<s>
In	O
most	O
cases	O
,	O
however	O
,	O
the	O
display	O
hardware	B-Architecture
supports	O
additional	O
modes	O
where	O
only	O
a	O
subset	O
of	O
those	O
colors	O
can	O
be	O
used	O
in	O
a	O
single	O
image	O
,	O
a	O
useful	O
technique	O
to	O
save	O
memory	B-General_Concept
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
CGA	B-Device
's	O
320×200	O
resolution	O
mode	O
could	O
show	O
only	O
four	O
of	O
the	O
16	O
colors	O
at	O
one	O
time	O
.	O
</s>
<s>
As	O
the	O
palettes	B-Data_Structure
were	O
entirely	O
proprietary	O
,	O
an	O
image	O
generated	O
on	O
one	O
platform	O
cannot	O
be	O
directly	O
viewed	O
properly	O
on	O
another	O
.	O
</s>
<s>
Examples	O
include	O
the	O
256-color	O
palette	B-Data_Structure
on	O
Atari	O
8-bit	O
machines	O
or	O
the	O
4,096	O
colors	O
of	O
the	O
VT241	B-Device
terminal	O
in	O
ReGIS	B-Application
graphics	O
mode	O
.	O
</s>
<s>
In	O
these	O
cases	O
it	O
was	O
common	O
for	O
the	O
image	O
to	O
only	O
allow	O
a	O
small	O
subset	O
of	O
the	O
total	O
number	O
of	O
colors	O
to	O
be	O
displayed	O
at	O
one	O
time	O
,	O
up	O
to	O
16	O
at	O
once	O
on	O
the	O
Atari	O
and	O
VT241	B-Device
.	O
</s>
<s>
Generally	O
,	O
these	O
systems	O
worked	O
identically	O
to	O
their	O
less-colorful	O
brethren	O
,	O
but	O
a	O
key	O
difference	O
was	O
that	O
there	O
were	O
too	O
many	O
colors	O
in	O
the	O
palette	B-Data_Structure
to	O
directly	O
encode	O
in	O
the	O
pixel	B-Algorithm
data	O
given	O
the	O
limited	O
amount	O
of	O
video	O
memory	B-General_Concept
.	O
</s>
<s>
Instead	O
,	O
they	O
used	O
a	O
colour	B-Data_Structure
look-up	I-Data_Structure
table	I-Data_Structure
(	O
CLUT	B-Data_Structure
)	O
where	O
each	O
pixel	B-Algorithm
's	O
data	O
pointed	O
to	O
an	O
entry	O
in	O
the	O
CLUT	B-Data_Structure
,	O
and	O
the	O
CLUT	B-Data_Structure
was	O
set	O
up	O
under	O
program	O
control	O
.	O
</s>
<s>
This	O
meant	O
that	O
the	O
image	O
CLUT	B-Data_Structure
data	O
had	O
to	O
be	O
stored	O
along	O
with	O
the	O
raw	O
image	O
data	O
in	O
order	O
to	O
be	O
able	O
to	O
re-produce	O
the	O
image	O
correctly	O
.	O
</s>
<s>
Hardware	B-Architecture
palettes	B-Data_Structure
based	O
on	O
component	O
video	O
colors	O
such	O
as	O
YPbPr	O
or	O
the	O
like	O
were	O
generally	O
replaced	O
in	O
the	O
mid	O
1980s	O
by	O
the	O
more	O
flexible	O
RGB	O
color	O
model	O
,	O
in	O
which	O
a	O
given	O
color	O
can	O
be	O
obtained	O
by	O
mixing	O
different	O
amounts	O
of	O
the	O
three	O
primary	O
colors	O
red	O
,	O
green	O
,	O
and	O
blue	O
.	O
</s>
<s>
Although	O
the	O
total	O
number	O
of	O
different	O
colors	O
depends	O
on	O
the	O
number	O
of	O
levels	O
per	O
primary	O
,	O
and	O
on	O
a	O
given	O
hardware	B-Architecture
implementation	O
(	O
a	O
9-bit	O
RGB	O
provides	O
512	O
combinations	O
,	O
a	O
12-bit	O
RGB	O
provides	O
4	O
,	O
096	O
,	O
and	O
so	O
on	O
)	O
,	O
in	O
this	O
model	O
digital-to-analog	O
converters	O
(	O
DAC	O
)	O
can	O
generate	O
the	O
colors	O
—	O
simplifying	O
the	O
hardware	B-Architecture
design	O
—	O
while	O
the	O
software	O
can	O
treat	O
the	O
number	O
per	O
levels	O
used	O
abstractly	O
and	O
manage	O
the	O
RGB	O
colors	O
in	O
a	O
device-independent	O
fashion	O
.	O
</s>
<s>
With	O
colors	O
stored	O
in	O
RGB	O
format	O
within	O
the	O
palettes	B-Data_Structure
of	O
indexed	B-Data_Structure
image	I-Data_Structure
files	O
,	O
any	O
image	O
can	O
be	O
displayed	O
(	O
through	O
appropriate	O
transformations	O
)	O
on	O
any	O
such	O
system	O
,	O
regardless	O
of	O
the	O
color	O
depth	O
used	O
in	O
the	O
hardware	B-Architecture
implementation	O
.	O
</s>
<s>
Today	O
,	O
display	O
hardware	B-Architecture
and	O
image	O
file	O
formats	O
that	O
deal	O
with	O
indexed	B-Data_Structure
color	I-Data_Structure
images	O
almost	O
exclusively	O
manage	O
colors	O
in	O
RGB	O
format	O
,	O
the	O
de	O
facto	O
standard	O
encoding	B-Algorithm
being	O
the	O
so-called	O
truecolor	O
or	O
24-bit	O
RGB	O
,	O
with	O
16,777,216	O
different	O
possible	O
colors	O
.	O
</s>
<s>
However	O
,	O
indexed	B-Data_Structure
color	I-Data_Structure
images	O
are	O
not	O
genuinely	O
constrained	O
to	O
a	O
24-bit	O
RGB	O
color	O
encoding	B-Algorithm
;	O
image	O
palettes	B-Data_Structure
can	O
hold	O
any	O
type	O
of	O
color	O
encoding	B-Algorithm
.	O
</s>
<s>
For	O
example	O
,	O
the	O
PDF	B-Application
file	I-Application
format	O
does	O
support	O
indexed	B-Data_Structure
color	I-Data_Structure
in	O
other	O
colorspaces	O
,	O
notably	O
CMYK	O
,	O
and	O
Adobe	B-Operating_System
Distiller	I-Operating_System
by	O
default	O
will	O
convert	O
images	O
to	O
indexed	B-Data_Structure
color	I-Data_Structure
whenever	O
the	O
total	O
number	O
of	O
colors	O
in	O
an	O
image	O
is	O
equal	O
to	O
or	O
less	O
than	O
256	O
.	O
</s>
<s>
When	O
using	O
RGB	O
,	O
the	O
TIFF	O
and	O
PNG	O
file	O
formats	O
can	O
optionally	O
store	O
the	O
RGB	O
triplets	O
with	O
a	O
precision	O
of	O
16-bit	O
(	O
65,536	O
levels	O
per	O
component	O
)	O
yielding	O
a	O
total	O
of	O
48	O
bits	O
per	O
pixel	B-Algorithm
.	O
</s>
<s>
A	O
proposed	O
extension	O
to	O
the	O
TIFF	O
Standard	O
allows	O
non-RGB	O
color	O
palettes	B-Data_Structure
,	O
but	O
this	O
was	O
never	O
implemented	O
in	O
software	O
due	O
to	O
technical	O
reasons	O
.	O
</s>
<s>
The	O
color	O
map	O
table	O
of	O
the	O
BMP	B-Device
file	I-Device
format	I-Device
indexed	B-Data_Structure
color	I-Data_Structure
mode	O
stores	O
its	O
entries	O
in	O
BGR	O
order	O
rather	O
than	O
RGB	O
,	O
and	O
has	O
(	O
in	O
the	O
current	O
version	O
)	O
an	O
additional	O
unused	O
byte	B-Application
for	O
padding	O
to	O
conform	O
to	O
32-bit	O
word	B-Application
alignment	I-Application
during	O
processing	O
,	O
but	O
it	O
is	O
essentially	O
still	O
a	O
24-bit	O
RGB	O
color	O
encoding	B-Algorithm
.	O
</s>
<s>
(	O
An	O
earlier	O
version	O
of	O
the	O
BMP	B-Device
format	I-Device
used	O
three	O
bytes	B-Application
per	O
24-bit	O
color	O
map	O
table	O
entry	O
,	O
and	O
many	O
files	O
in	O
that	O
format	O
are	O
still	O
in	O
circulation	O
,	O
so	O
many	O
modern	O
programs	O
that	O
read	O
BMP	B-Device
files	I-Device
support	O
both	O
variations	O
.	O
)	O
</s>
<s>
Except	O
for	O
very	O
low	O
resolution	O
graphic	O
modes	O
,	O
early	O
home	O
and	O
personal	B-Device
computers	I-Device
rarely	O
implemented	O
an	O
"	O
all-pixels-addressable	O
"	O
design	O
-	O
that	O
is	O
,	O
the	O
ability	O
to	O
change	O
a	O
single	O
pixel	B-Algorithm
to	O
any	O
of	O
the	O
available	O
colors	O
independently	O
.	O
</s>
<s>
Their	O
limitations	O
came	O
from	O
employing	O
separate	O
color	O
attribute	O
or	O
color	O
RAM	B-Architecture
areas	O
,	O
leading	O
to	O
attribute	B-Algorithm
clash	I-Algorithm
effects	O
.	O
</s>
<s>
Also	O
,	O
the	O
pixel	B-Algorithm
bits	O
and/or	O
the	O
scan	O
lines	O
of	O
the	O
video	O
memory	B-General_Concept
were	O
commonly	O
arranged	O
in	O
odd	O
ways	O
convenient	O
for	O
the	O
video	O
generator	O
hardware	B-Architecture
(	O
thus	O
saving	O
hardware	B-Architecture
costs	O
in	O
a	O
cost-competitive	O
market	O
)	O
,	O
but	O
sometimes	O
creating	O
difficulty	O
for	O
the	O
people	O
writing	O
graphics	O
programs	O
.	O
</s>
<s>
A	O
pixel	B-Algorithm
's	O
bits	O
in	O
indexed-color	B-Data_Structure
,	O
all-pixel-addressable	O
images	O
are	O
not	O
always	O
contiguous	O
in	O
video	O
memory	B-General_Concept
or	O
image	O
files	O
(	O
i.e.	O
,	O
chunky	B-General_Concept
organization	O
is	O
not	O
always	O
used	O
.	O
)	O
</s>
<s>
are	O
arranged	O
as	O
a	O
series	O
of	O
bit	O
planes	O
(	O
in	O
a	O
configuration	O
called	O
planar	B-Device
)	O
,	O
in	O
which	O
the	O
related	O
bits	O
of	O
a	O
single	O
pixel	B-Algorithm
are	O
split	O
among	O
several	O
independent	O
bitmaps	O
.	O
</s>
<s>
Thus	O
,	O
the	O
pixel	B-Algorithm
bits	O
are	O
conceptually	O
aligned	O
along	O
the	O
3D	O
Z-axis	O
.	O
</s>
<s>
(	O
The	O
"	O
depth	O
"	O
concept	O
here	O
is	O
not	O
the	O
same	O
as	O
that	O
of	O
pixel	B-Algorithm
depth	O
.	O
)	O
</s>
<s>
Early	O
image	O
file	O
formats	O
,	O
such	O
as	O
PIC	O
,	O
stored	O
little	O
more	O
than	O
a	O
bare	O
memory	B-Error_Name
dump	I-Error_Name
of	O
the	O
video	B-Algorithm
buffer	I-Algorithm
of	O
a	O
given	O
machine	O
.	O
</s>
<s>
Some	O
indexed-color	B-Data_Structure
image	O
file	O
formats	O
such	O
as	O
Graphics	O
Interchange	O
Format	O
(	O
GIF	O
)	O
allow	O
the	O
image	O
's	O
scan	O
lines	O
to	O
be	O
arranged	O
in	O
interleaved	O
fashion	O
(	O
not	O
linear	O
order	O
)	O
,	O
which	O
allows	O
a	O
low	O
resolution	O
version	O
of	O
the	O
image	O
to	O
appear	O
on	O
screen	O
while	O
it	O
is	O
still	O
downloading	O
,	O
so	O
that	O
the	O
computer	O
user	O
can	O
gain	O
an	O
idea	O
of	O
its	O
contents	O
during	O
the	O
seconds	O
before	O
the	O
whole	O
image	O
arrives	O
.	O
</s>
<s>
Indexed	B-Data_Structure
color	I-Data_Structure
saves	O
a	O
lot	O
of	O
memory	B-General_Concept
,	O
storage	O
space	O
,	O
and	O
transmission	O
time	O
:	O
using	O
truecolor	O
,	O
each	O
pixel	B-Algorithm
needs	O
24	O
bits	O
,	O
or	O
3	O
bytes	B-Application
.	O
</s>
<s>
A	O
typical	O
640×480	O
VGA	B-Protocol
resolution	O
truecolor	O
uncompressed	O
image	O
needs	O
640×480×3	O
=	O
921,600	O
bytes	B-Application
(	O
900	O
KiB	O
)	O
.	O
</s>
<s>
Limiting	O
the	O
image	O
colors	O
to	O
256	O
,	O
every	O
pixel	B-Algorithm
needs	O
only	O
8	O
bits	O
,	O
or	O
1	O
byte	B-Application
each	O
,	O
so	O
the	O
example	O
image	O
now	O
needs	O
only	O
640×480×1	O
=	O
307,200	O
bytes	B-Application
(	O
300	O
KiB	O
)	O
,	O
plus	O
256×3	O
=	O
768	O
additional	O
bytes	B-Application
to	O
store	O
the	O
palette	B-Data_Structure
map	O
in	O
itself	O
(	O
assuming	O
RGB	O
)	O
,	O
approximately	O
one	O
third	O
of	O
the	O
original	O
size	O
.	O
</s>
<s>
Smaller	O
palettes	B-Data_Structure
(	O
4-bit	O
16	O
colors	O
,	O
2-bit	O
4	O
colors	O
)	O
can	O
pack	O
the	O
pixels	B-Algorithm
even	O
more	O
(	O
to	O
one	O
sixth	O
or	O
one	O
twelfth	O
)	O
,	O
obviously	O
at	O
cost	O
of	O
color	O
accuracy	O
.	O
</s>
<s>
Indexed	B-Data_Structure
color	I-Data_Structure
was	O
widely	O
used	O
in	O
early	O
personal	B-Device
computers	I-Device
and	O
display	B-Device
adapters	I-Device
 '	O
hardware	B-Architecture
to	O
reduce	O
costs	O
(	O
mainly	O
by	O
requiring	O
fewer	O
of	O
the	O
then-expensive	O
RAM	B-Architecture
chips	I-Architecture
)	O
but	O
also	O
for	O
convenient	O
image	O
management	O
with	O
limited-power	O
CPUs	B-Device
(	O
of	O
the	O
order	O
of	O
4	O
to	O
8	O
MHz	O
)	O
,	O
file	B-Device
storage	I-Device
(	O
cassette	O
tapes	O
and	O
low	O
density	O
floppy	B-Device
disks	I-Device
)	O
.	O
</s>
<s>
Notable	O
computer	O
graphics	O
systems	O
extensively	O
(	O
or	O
even	O
exclusively	O
)	O
using	O
pseudocolor	O
palettes	B-Data_Structure
in	O
the	O
1980s	O
include	O
CGA	B-Device
,	O
EGA	B-Device
,	O
and	O
VGA	B-Protocol
(	O
for	O
IBM	O
PC	O
compatibles	O
)	O
,	O
the	O
Atari	B-Device
ST	I-Device
,	O
and	O
Amiga	B-Device
's	O
OCS	B-Device
and	O
AGA	B-Device
.	O
</s>
<s>
Later	O
,	O
the	O
HTML	B-Language
web	O
pages	O
used	O
the	O
GIF	O
along	O
with	O
other	O
indexed	O
color-supporting	O
file	O
formats	O
such	O
as	O
PNG	O
,	O
to	O
exchange	O
limited-color	O
images	O
quickly	O
and	O
store	O
them	O
in	O
limited	O
storage	O
space	O
.	O
</s>
<s>
Most	O
image	O
file	O
formats	O
that	O
support	O
indexed	B-Data_Structure
color	I-Data_Structure
images	O
also	O
commonly	O
support	O
some	O
compression	B-General_Concept
scheme	O
,	O
enhancing	O
their	O
ability	O
to	O
store	O
the	O
images	O
in	O
smaller	O
files	O
.	O
</s>
<s>
Interesting	O
colorized	O
and	O
artistic	O
effects	O
can	O
be	O
easily	O
achieved	O
by	O
altering	O
the	O
color	O
palette	B-Data_Structure
of	O
indexed	B-Data_Structure
color	I-Data_Structure
images	O
,	O
for	O
example	O
to	O
produce	O
colorized	O
sepia	O
tone	O
images	O
.	O
</s>
<s>
Due	O
to	O
the	O
separate	O
nature	O
of	O
the	O
associated	O
palette	B-Data_Structure
element	I-Data_Structure
of	O
the	O
indexed	B-Data_Structure
color	I-Data_Structure
images	O
,	O
they	O
are	O
ideal	O
to	O
remap	O
grayscale	O
images	O
into	O
false	B-Application
color	I-Application
ones	O
through	O
the	O
use	O
of	O
false	B-Application
color	I-Application
palettes	B-Data_Structure
.	O
</s>
<s>
By	O
manipulating	O
the	O
color	O
hardware	B-Architecture
registers	O
(	O
Color	B-Data_Structure
look-up	I-Data_Structure
table	I-Data_Structure
or	O
CLUT	B-Data_Structure
)	O
of	O
the	O
display	B-Device
adapter	I-Device
in	O
the	O
indexed	B-Data_Structure
color	I-Data_Structure
graphic	O
modes	O
,	O
full-screen	O
color-animation	O
effects	O
can	O
be	O
achieved	O
without	O
redrawing	O
the	O
image	O
-	O
that	O
is	O
,	O
at	O
low	O
CPU	B-Device
time	O
cost	O
;	O
a	O
single	O
change	O
of	O
the	O
register	O
values	O
affects	O
the	O
whole	O
screen	O
at	O
once	O
.	O
</s>
<s>
Color-map	O
animation	O
,	O
also	O
known	O
as	O
Color	B-Device
cycling	I-Device
,	O
is	O
extensively	O
used	O
in	O
the	O
demoscene	O
.	O
</s>
<s>
The	O
Microsoft	O
Windows	O
boot	O
logo	O
screen	O
in	O
Windows	O
95	O
,	O
98	O
,	O
ME	O
,	O
and	O
2000	O
Professional	O
(	O
which	O
uses	O
VGA	B-Protocol
320x200x256	O
color	O
display	O
mode	O
because	O
it	O
is	O
the	O
greatest	O
common	O
denominator	O
on	O
all	O
PCs	B-Device
)	O
employs	O
this	O
technique	O
for	O
the	O
scrolling	O
gradient	O
bar	O
across	O
the	O
bottom	O
of	O
the	O
screen	O
;	O
the	O
picture	O
is	O
a	O
static	O
image	O
with	O
no	O
pixels	B-Algorithm
rewritten	O
after	O
it	O
is	O
initially	O
displayed	O
.	O
</s>
<s>
The	O
main	O
disadvantage	O
of	O
using	O
indexed	B-Data_Structure
color	I-Data_Structure
is	O
the	O
limited	O
set	O
of	O
simultaneous	O
colors	O
per	O
image	O
.	O
</s>
<s>
Small	O
4	O
-	O
or	O
16-color	O
palettes	B-Data_Structure
are	O
still	O
acceptable	O
for	O
little	O
images	O
(	O
icons	O
)	O
or	O
very	O
simple	O
graphics	O
,	O
but	O
to	O
reproduce	O
real	O
life	O
images	O
they	O
become	O
nearly	O
useless	O
.	O
</s>
<s>
Some	O
techniques	O
,	O
such	O
as	O
color	B-Algorithm
quantization	I-Algorithm
,	O
anti-aliasing	B-Algorithm
and	O
dithering	O
combined	O
together	O
can	O
create	O
indexed	O
256-color	O
images	O
comparable	O
to	O
the	O
original	O
up	O
to	O
an	O
acceptable	O
level	O
.	O
</s>
<s>
Indexed	B-Data_Structure
color	I-Data_Structure
images	O
are	O
heavily	O
dependent	O
on	O
their	O
own	O
color	O
palettes	B-Data_Structure
.	O
</s>
<s>
Except	O
for	O
a	O
few	O
well	O
known	O
fixed-color	O
palettes	B-Data_Structure
(	O
such	O
as	O
that	O
of	O
the	O
Color	B-Device
Graphics	I-Device
Adapter	I-Device
—	O
CGA	B-Device
)	O
,	O
raw	O
image	O
data	O
and/or	O
color	O
map	O
tables	O
cannot	O
be	O
reliably	O
exchanged	O
between	O
different	O
image	O
files	O
without	O
some	O
kind	O
of	O
intermediate	O
mapping	O
.	O
</s>
<s>
Also	O
,	O
if	O
the	O
original	O
color	O
palette	B-Data_Structure
for	O
a	O
given	O
indexed	B-Data_Structure
image	I-Data_Structure
is	O
lost	O
,	O
it	O
can	O
be	O
nearly	O
impossible	O
to	O
restore	O
it	O
.	O
</s>
<s>
Here	O
is	O
an	O
example	O
of	O
what	O
happens	O
when	O
an	O
indexed	B-Data_Structure
color	I-Data_Structure
image	O
(	O
the	O
previous	O
parrot	O
)	O
has	O
been	O
associated	O
with	O
an	O
incorrect	O
color	O
palette	B-Data_Structure
:	O
</s>
<s>
Indexed	B-Data_Structure
color	I-Data_Structure
graphic	O
modes	O
for	O
display	B-Device
adapters	I-Device
have	O
the	O
16	O
-	O
or	O
256-color	O
limit	O
imposed	O
by	O
hardware	B-Architecture
.	O
</s>
<s>
Indexed	B-Data_Structure
color	I-Data_Structure
images	O
with	O
rich	O
but	O
incompatible	O
palettes	B-Data_Structure
can	O
only	O
be	O
accurately	O
displayed	O
one	O
at	O
a	O
time	O
,	O
as	O
in	O
a	O
slideshow	O
.	O
</s>
<s>
When	O
it	O
is	O
necessary	O
to	O
show	O
multiple	O
images	O
together	O
,	O
as	O
in	O
a	O
mosaic	O
of	O
thumbnails	O
,	O
a	O
common	O
or	O
master	O
palette	B-Data_Structure
is	O
often	O
used	O
,	O
which	O
encompasses	O
as	O
many	O
different	O
hues	O
as	O
possible	O
into	O
a	O
single	O
set	O
,	O
thereby	O
limiting	O
the	O
overall	O
accurate	O
color	O
availability	O
.	O
</s>
<s>
The	O
following	O
image	O
is	O
a	O
mosaic	O
of	O
four	O
different	O
indexed	B-Data_Structure
color	I-Data_Structure
images	O
rendered	O
with	O
a	O
single	O
shared	O
master	O
palette	B-Data_Structure
of	O
6-8-5	O
levels	O
RGB	O
plus	O
16	O
additional	O
grays	O
.	O
</s>
<s>
Note	O
the	O
limited	O
range	O
of	O
colors	O
used	O
for	O
every	O
image	O
,	O
and	O
how	O
many	O
palette	B-Data_Structure
entries	I-Data_Structure
are	O
left	O
unused	O
.	O
</s>
<s>
Many	O
indexed	B-Data_Structure
color	I-Data_Structure
display	O
devices	O
do	O
not	O
reach	O
the	O
24-bit	O
limit	O
for	O
the	O
full	O
RGB	O
palette	B-Data_Structure
.	O
</s>
<s>
The	O
VGA	B-Protocol
for	O
IBM	O
PC	O
compatibles	O
,	O
for	O
example	O
,	O
only	O
provides	O
an	O
18-bit	O
RGB	O
palette	B-Data_Structure
with	O
262,144	O
different	O
possible	O
colors	O
in	O
both	O
16	O
-	O
and	O
256	O
-	O
indexed	B-Data_Structure
color	I-Data_Structure
graphic	O
modes	O
.	O
</s>
<s>
Some	O
image	O
editing	O
software	O
allows	O
gamma	O
correction	O
to	O
be	O
applied	O
to	O
a	O
palette	B-Data_Structure
for	O
indexed	B-Data_Structure
color	I-Data_Structure
image	O
files	O
.	O
</s>
<s>
It	O
is	O
better	O
to	O
apply	O
the	O
gamma	O
correction	O
with	O
the	O
display	O
hardware	B-Architecture
(	O
most	O
modern	O
display	B-Device
adapters	I-Device
support	O
this	O
feature	O
)	O
,	O
or	O
as	O
an	O
active	O
intermediate	O
step	O
of	O
the	O
rendering	O
software	O
through	O
color	O
management	O
,	O
which	O
preserves	O
the	O
original	O
color	O
values	O
.	O
</s>
<s>
Only	O
when	O
the	O
indexed	B-Data_Structure
color	I-Data_Structure
images	O
are	O
intended	O
for	O
systems	O
that	O
lack	O
any	O
kind	O
of	O
color	O
calibration	O
,	O
and	O
they	O
are	O
not	O
intended	O
to	O
be	O
cross-platform	O
,	O
gamma	O
correction	O
may	O
be	O
applied	O
to	O
the	O
color	B-Data_Structure
table	I-Data_Structure
itself	O
.	O
</s>
<s>
These	O
are	O
some	O
of	O
the	O
most	O
representative	O
image	O
file	O
formats	O
that	O
support	O
indexed	B-Data_Structure
color	I-Data_Structure
modes	O
.	O
</s>
<s>
truecolor	O
)	O
,	O
but	O
only	O
the	O
indexed	B-Data_Structure
color	I-Data_Structure
modes	O
are	O
listed	O
here	O
.	O
</s>
<s>
NOTE	O
:	O
most	O
of	O
the	O
formats	O
will	O
also	O
support	O
a	O
color	B-Data_Structure
table	I-Data_Structure
with	O
fewer	O
colors	O
than	O
the	O
maximum	O
that	O
a	O
given	O
bit	O
depth	O
can	O
offer	O
.	O
</s>
<s>
*	O
64	O
-	O
(	O
true	O
,	O
not	O
EHB	O
)	O
,	O
128	O
-	O
and	O
256-color	O
modes	O
only	O
available	O
for	O
the	O
AGA	B-Device
Amiga	B-Device
chipset	O
.	O
</s>
<s>
**	O
Native	O
support	O
for	O
proprietary	O
compression	B-General_Concept
schemes	O
.	O
</s>
<s>
***	O
RLE	B-Algorithm
with	O
optional	O
proprietary	O
Delta-leaps	O
.	O
</s>
