<s>
Visual	O
information	O
is	O
always	O
contained	O
in	O
some	O
kind	O
of	O
visual	O
contrast	O
,	O
thus	O
contrast	O
is	O
an	O
essential	O
performance	O
feature	O
of	O
electronic	B-Device
visual	I-Device
displays	I-Device
.	O
</s>
<s>
The	O
contrast	O
of	O
electronic	B-Device
visual	I-Device
displays	I-Device
depends	O
on	O
the	O
electrical	O
driving	O
(	O
analog	O
or	O
digital	O
input	O
signal	O
)	O
,	O
on	O
the	O
ambient	O
illumination	O
and	O
on	O
the	O
direction	B-Device
of	I-Device
observation	I-Device
(	O
i.e.	O
</s>
<s>
viewing	B-Device
direction	I-Device
)	O
.	O
</s>
<s>
This	O
ratio	O
,	O
often	O
called	O
contrast	O
ratio	O
,	O
CR	O
,	O
(	O
actually	O
being	O
a	O
luminance	O
ratio	O
)	O
,	O
is	O
often	O
used	O
for	O
high	O
luminances	O
and	O
for	O
specification	O
of	O
the	O
contrast	O
of	O
electronic	B-Device
visual	I-Device
display	I-Device
devices	O
.	O
</s>
<s>
Another	O
contrast	O
definition	O
is	O
a	O
practical	O
application	O
of	O
Weber	O
contrast	O
,	O
sometimes	O
found	O
in	O
the	O
electronic	B-Device
displays	I-Device
field	O
,	O
K	O
or	O
CW	O
,	O
is	O
:	O
</s>
<s>
A	O
metric	O
for	O
color	O
contrast	O
often	O
used	O
in	O
the	O
electronic	B-Device
displays	I-Device
field	O
is	O
the	O
color	O
difference	O
ΔE*uv	O
or	O
ΔE*ab	O
.	O
</s>
<s>
Such	O
loading	O
effects	O
can	O
be	O
found	O
in	O
CRT-displays	O
and	O
in	O
PDPs	O
.	O
</s>
<s>
thumb|left|repetitive	O
impulse	O
response	O
of	O
an	O
LCD-monitorThis	O
illustration	O
shows	O
the	O
repetitive	O
impulse	O
response	O
between	O
several	O
states	O
of	O
gray	O
when	O
each	O
state	O
is	O
applied	O
for	O
one	O
frame	O
only	O
.	O
</s>
<s>
This	O
is	O
a	O
technique	O
for	O
expanding	O
the	O
contrast	O
of	O
LCD-screens	B-Device
.	O
</s>
<s>
LCD-screens	B-Device
comprise	O
a	O
backlight	O
unit	O
which	O
is	O
permanently	O
emitting	O
light	O
and	O
an	O
LCD-panel	O
in	O
front	O
of	O
it	O
which	O
modulates	O
transmission	O
of	O
light	O
with	O
respect	O
to	O
intensity	O
and	O
chromaticity	O
.	O
</s>
<s>
In	O
order	O
to	O
increase	O
the	O
contrast	O
of	O
such	O
LCD-screens	B-Device
the	O
backlight	O
can	O
be	O
(	O
globally	O
)	O
dimmed	O
when	O
the	O
image	O
to	O
be	O
displayed	O
is	O
dark	O
(	O
i.e.	O
</s>
<s>
There	O
is	O
quite	O
some	O
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
required	O
for	O
implementation	O
of	O
the	O
dynamic	O
contrast	O
control	O
technique	O
in	O
a	O
way	O
that	O
is	O
pleasing	O
to	O
the	O
human	O
visual	O
system	O
(	O
e.g.	O
</s>
<s>
High-dynamic-range	O
(	O
HDR	O
)	O
LCDs	B-Device
are	O
using	O
that	O
technique	O
in	O
order	O
to	O
realize	O
(	O
static	O
)	O
contrast	O
values	O
in	O
the	O
range	O
of	O
CR	O
>	O
100.000	O
.	O
</s>
<s>
All	O
emissive	O
electronic	B-Device
displays	I-Device
(	O
e.g.	O
</s>
<s>
If	O
the	O
reflective	O
properties	O
of	O
the	O
projection	O
screen	O
(	O
usually	O
depending	O
on	O
direction	O
)	O
are	O
included	O
in	O
the	O
measurement	O
,	O
the	O
luminance	O
reflected	O
from	O
the	O
centers	O
of	O
the	O
rectangles	O
has	O
to	O
be	O
measured	O
for	O
a	O
(	O
set	O
of	O
)	O
specific	O
directions	B-Device
of	I-Device
observation	I-Device
.	O
</s>
<s>
Luminance	O
,	O
contrast	O
and	O
chromaticity	O
of	O
LCD-screens	B-Device
is	O
usually	O
varying	O
with	O
the	O
direction	B-Device
of	I-Device
observation	I-Device
(	O
i.e.	O
</s>
<s>
viewing	B-Device
direction	I-Device
)	O
.	O
</s>
<s>
The	O
variation	O
of	O
electro-optical	O
characteristics	O
with	O
viewing	B-Device
direction	I-Device
can	O
be	O
measured	O
sequentially	O
by	O
mechanical	O
scanning	O
of	O
the	O
viewing	B-Device
cone	I-Device
(	O
gonioscopic	O
approach	O
)	O
or	O
by	O
simultaneous	O
measurements	O
based	O
on	O
conoscopy	O
.	O
</s>
