<s>
The	O
shadow	B-General_Concept
mask	I-General_Concept
is	O
one	O
of	O
the	O
two	O
technologies	O
used	O
in	O
the	O
manufacture	O
of	O
cathode-ray	B-Device
tube	I-Device
(	O
CRT	O
)	O
televisions	O
and	O
computer	B-Device
monitors	I-Device
which	O
produce	O
clear	O
,	O
focused	O
color	O
images	O
.	O
</s>
<s>
The	O
other	O
approach	O
is	O
the	O
aperture	B-General_Concept
grille	I-General_Concept
,	O
better	O
known	O
by	O
its	O
trade	O
name	O
,	O
Trinitron	O
.	O
</s>
<s>
All	O
early	O
color	O
televisions	O
and	O
the	O
majority	O
of	O
CRT	O
computer	B-Device
monitors	I-Device
used	O
shadow	B-General_Concept
mask	I-General_Concept
technology	O
.	O
</s>
<s>
Both	O
of	O
these	O
technologies	O
are	O
largely	O
obsolete	O
,	O
having	O
been	O
increasingly	O
replaced	O
since	O
the	O
1990s	O
by	O
the	O
liquid-crystal	B-Device
display	I-Device
(	O
LCD	B-Device
)	O
.	O
</s>
<s>
A	O
shadow	B-General_Concept
mask	I-General_Concept
is	O
a	O
metal	O
plate	O
punched	O
with	O
tiny	O
holes	O
that	O
separate	O
the	O
colored	O
phosphors	O
in	O
the	O
layer	O
behind	O
the	O
front	O
glass	O
of	O
the	O
screen	O
.	O
</s>
<s>
Shadow	B-General_Concept
masks	I-General_Concept
are	O
made	O
by	O
photochemical	O
machining	O
,	O
a	O
technique	O
that	O
allows	O
for	O
the	O
drilling	O
of	O
small	O
holes	O
on	O
metal	O
sheets	O
.	O
</s>
<s>
A	O
red	O
,	O
a	O
green	O
,	O
and	O
a	O
blue	O
phosphor	O
are	O
generally	O
arranged	O
in	O
a	O
triangular	O
shape	O
(	O
sometimes	O
called	O
a	O
"	O
triad	B-General_Concept
"	O
)	O
.	O
</s>
<s>
(	O
This	O
is	O
conceptually	O
similar	O
to	O
a	O
DLP	B-General_Concept
based	O
projection	O
display	O
where	O
a	O
single	O
DLP	B-General_Concept
device	O
is	O
used	O
for	O
all	O
three	O
color	O
channels	O
.	O
)	O
</s>
<s>
The	O
remaining	O
color	O
information	O
was	O
separately	O
encoded	O
into	O
the	O
signal	O
as	O
a	O
high-frequency	O
modulation	B-Application
to	O
produce	O
a	O
composite	O
video	O
signal	O
.	O
</s>
<s>
But	O
it	O
was	O
RCA	O
's	O
success	O
with	O
the	O
shadow	B-General_Concept
mask	I-General_Concept
that	O
dampened	O
most	O
of	O
these	O
efforts	O
.	O
</s>
<s>
Until	O
1968	O
,	O
every	O
color	O
television	O
sold	O
used	O
the	O
RCA	O
shadow	B-General_Concept
mask	I-General_Concept
concept	O
,	O
in	O
the	O
spring	O
of	O
that	O
year	O
Sony	O
introduced	O
their	O
first	O
Trinitron	O
sets	O
.	O
</s>
<s>
To	O
produce	O
an	O
image	O
as	O
bright	O
as	O
the	O
one	O
on	O
a	O
traditional	O
B&W	O
television	O
,	O
the	O
electron	O
guns	O
in	O
this	O
hypothetical	O
shadow	B-General_Concept
mask	I-General_Concept
system	O
would	O
have	O
to	O
be	O
five	O
times	O
more	O
powerful	O
.	O
</s>
<s>
The	O
energy	O
the	O
shadow	B-General_Concept
mask	I-General_Concept
absorbs	O
from	O
the	O
electron	O
gun	O
in	O
normal	O
operation	O
causes	O
it	O
to	O
heat	O
up	O
and	O
expand	O
,	O
which	O
leads	O
to	O
blurred	O
or	O
discolored	O
images	O
(	O
see	O
doming	O
)	O
.	O
</s>
<s>
During	O
development	O
,	O
RCA	O
was	O
not	O
sure	O
that	O
they	O
could	O
make	O
the	O
shadow	B-General_Concept
mask	I-General_Concept
system	O
work	O
.	O
</s>
<s>
RCA	O
had	O
,	O
by	O
this	O
time	O
,	O
produced	O
experimental	O
shadow	B-General_Concept
mask	I-General_Concept
sets	O
that	O
were	O
an	O
enormous	O
leap	O
in	O
quality	O
over	O
any	O
competitors	O
.	O
</s>
<s>
Shadow	B-General_Concept
masks	I-General_Concept
are	O
made	O
using	O
a	O
photochemical	O
machining	O
process	O
.	O
</s>
<s>
The	O
shadow	B-General_Concept
mask	I-General_Concept
is	O
installed	O
to	O
the	O
screen	O
using	O
metal	O
pieces	O
or	O
a	O
rail	O
or	O
frame	O
that	O
is	O
fused	O
to	O
the	O
funnel	O
or	O
the	O
screen	O
glass	O
respectively	O
,	O
holding	O
the	O
shadow	B-General_Concept
mask	I-General_Concept
in	O
tension	O
to	O
minimize	O
warping	O
(	O
if	O
the	O
mask	O
is	O
flat	O
,	O
used	O
in	O
flat	O
screen	O
CRT	O
computer	B-Device
monitors	I-Device
)	O
and	O
allowing	O
for	O
higher	O
image	O
brightness	O
and	O
contrast	O
.	O
</s>
<s>
Bimetal	O
springs	O
may	O
be	O
used	O
in	O
CRTs	O
used	O
in	O
TVs	O
to	O
compensate	O
for	O
warping	O
that	O
occurs	O
as	O
the	O
electron	O
beam	O
heats	O
the	O
shadow	B-General_Concept
mask	I-General_Concept
,	O
causing	O
thermal	O
expansion	O
.	O
</s>
<s>
Doming	O
problems	O
due	O
to	O
thermal	O
expansion	O
of	O
the	O
shadow	B-General_Concept
mask	I-General_Concept
were	O
solved	O
in	O
several	O
ways	O
.	O
</s>
<s>
Bi-metallic	O
shadow	B-General_Concept
masks	I-General_Concept
,	O
where	O
differential	O
expansion	O
rates	O
offset	O
the	O
issue	O
,	O
became	O
common	O
in	O
the	O
late	O
1960s	O
.	O
</s>
<s>
In	O
manufacturing	O
color	O
CRTs	O
,	O
the	O
shadow	B-General_Concept
masks	I-General_Concept
or	O
aperture	B-General_Concept
grilles	I-General_Concept
were	O
also	O
used	O
to	O
expose	O
photoresist	O
on	O
the	O
faceplate	O
to	O
ultraviolet	O
light	O
sources	O
,	O
accurately	O
positioned	O
to	O
simulate	O
arriving	O
electrons	O
for	O
one	O
color	O
at	O
a	O
time	O
.	O
</s>
<s>
(	O
The	O
shadow	B-General_Concept
mask	I-General_Concept
or	O
aperture	B-General_Concept
grille	I-General_Concept
had	O
to	O
be	O
removable	O
and	O
accurately	O
re-positionable	O
for	O
this	O
process	O
to	O
succeed	O
.	O
)	O
</s>
