<s>
A	O
flicker	B-Device
fixer	I-Device
or	O
scan	B-Device
doubler	I-Device
is	O
a	O
piece	O
of	O
computer	B-Architecture
hardware	I-Architecture
that	O
de-interlaces	O
an	O
output	O
video	O
signal	O
.	O
</s>
<s>
The	O
flicker	B-Device
fixer	I-Device
accomplishes	O
this	O
by	O
adjusting	O
the	O
timing	O
of	O
the	O
natively	O
interlaced	O
video	O
signal	O
to	O
suit	O
the	O
needs	O
of	O
a	O
progressive	O
display	O
Ex	O
:	O
CRT	B-Device
computer	O
monitor	O
.	O
</s>
<s>
Flicker	B-Device
fixers	I-Device
in	O
essence	O
create	O
a	O
progressive	O
frame	O
of	O
video	O
from	O
two	O
interlaced	O
fields	O
of	O
video	O
.	O
</s>
<s>
Flicker	B-Device
fixers	I-Device
sample	B-Algorithm
the	O
NTSC/PAL	O
output	O
from	O
the	O
output	O
device	O
and	O
store	O
each	O
scan	O
line	O
from	O
the	O
field	O
currently	O
being	O
displayed	O
in	O
RAM	B-Architecture
while	O
simultaneously	O
outputting	O
the	O
line	O
alternately	O
with	O
the	O
corresponding	O
neighboring	O
lines	O
from	O
the	O
field	O
stored	O
previously	O
(	O
weaving	O
)	O
.	O
</s>
<s>
Some	O
more	O
advanced	O
flicker	B-Device
fixers	I-Device
integrated	O
in	O
add-on	O
graphics	O
cards	O
use	O
more	O
sophisticated	O
methods	O
.	O
</s>
<s>
Outputting	O
the	O
image	O
at	O
double	B-Device
scan	I-Device
rate	O
essentially	O
composes	O
a	O
progressive	O
display	O
with	O
all	O
lines	O
from	O
both	O
fields	O
at	O
full	O
vertical	O
refresh	O
rate	O
.	O
</s>
<s>
This	O
promotes	O
the	O
horizontal	O
frequency	O
of	O
the	O
signal	O
from	O
15.734kHz	O
to	O
31.47kHz	O
(	O
in	O
the	O
NTSC	O
case	O
,	O
numbers	O
for	O
PAL	B-Language
are	O
slightly	O
lower	O
)	O
,	O
which	O
can	O
be	O
the	O
used	O
to	O
drive	O
a	O
VGA	B-Protocol
monitor	I-Protocol
from	O
an	O
output	O
device	O
.	O
</s>
<s>
One	O
computer	O
capable	O
of	O
producing	O
an	O
interlaced	O
image	O
is	O
the	O
Amiga	B-Device
.	O
</s>
<s>
The	O
Amiga	B-Device
's	O
default	O
video	O
mode	O
is	O
PAL	B-Language
or	O
NTSC	O
.	O
</s>
<s>
NTSC	O
and	O
PAL	B-Language
interlaced	O
screens	O
have	O
two	O
fields	O
called	O
odd	O
and	O
even	O
.	O
</s>
<s>
The	O
fields	O
switch	O
every	O
60th	O
of	O
a	O
second	O
on	O
NTSC	O
,	O
or	O
50th	O
of	O
a	O
second	O
on	O
PAL	B-Language
,	O
which	O
allows	O
for	O
higher	O
resolution	O
while	O
using	O
a	O
narrower	O
signal	B-Algorithm
bandwidth	I-Algorithm
than	O
full	O
50	O
or	O
60	O
FPS	O
progressive	O
video	O
would	O
require	O
,	O
but	O
it	O
can	O
also	O
produce	O
an	O
alarming	O
jittering	O
effect	O
for	O
graphics	O
with	O
high	O
contrast	O
details	O
between	O
fields	O
.	O
</s>
<s>
This	O
NTSC/PAL	O
compatibility	O
gave	O
the	O
Amiga	B-Device
a	O
distinct	O
edge	O
in	O
uses	O
such	O
as	O
television	O
production	O
and	O
gaming	O
,	O
but	O
since	O
the	O
original	O
Amigas	B-Device
were	O
unable	O
to	O
produce	O
vertically	O
high-resolution	O
displays	O
without	O
flickering	O
this	O
was	O
unsuitable	O
for	O
office-like	O
usage	O
where	O
one	O
might	O
need	O
to	O
work	O
with	O
a	O
clear	O
high-resolution	O
image	O
for	O
several	O
hours	O
.	O
</s>
<s>
Flicker	B-Device
fixers	I-Device
were	O
devised	O
to	O
remedy	O
this	O
.	O
</s>
<s>
The	O
later	O
iteration	O
of	O
the	O
Amiga	B-Device
-	O
the	O
Amiga	B-Device
3000	I-Device
had	O
a	O
custom	O
chip	O
called	O
Amber	O
which	O
could	O
perform	O
flicker-fixing	O
on	O
any	O
signal	O
.	O
</s>
<s>
The	O
ECS	B-Device
and	O
AGA	B-Device
chipset	B-Device
could	O
also	O
output	O
VGA	B-Protocol
display	O
modes	O
.	O
</s>
<s>
Commodore	O
offered	O
the	O
A2320	O
Display	O
Enhancer	O
Board	O
for	O
this	O
purpose	O
,	O
The	O
board	O
fit	O
neatly	O
in	O
a	O
video	B-Protocol
graphics	I-Protocol
adapter	I-Protocol
slot	O
on	O
the	O
A2000	O
series	O
computer	O
.	O
</s>
<s>
It	O
supported	O
the	O
new	O
video	O
modes	O
offered	O
by	O
the	O
Enhanced	B-Device
Chip	I-Device
Set	I-Device
(	O
ECS	B-Device
)	O
and	O
AmigaOS	B-Application
2.0	O
,	O
including	O
the	O
Productivity	O
Mode	O
.	O
</s>
<s>
Also	O
,	O
the	O
earlier	O
A2024	O
'	O
Hedley	O
 '	O
greyscale	O
monitor	O
featured	O
an	O
integrated	O
flicker	B-Device
fixer	I-Device
,	O
supporting	O
up	O
to	O
8	O
shades	O
of	O
grey	O
.	O
</s>
