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Understanding Contrast Ratio
Self explanatory really, use a real image and see what the projector can do
with the ratio between the 100% black and 100% white points.
Blacks
can only be as black as projection screen is in the ambient light:
If your room is not pitch black the screen will be reflecting some light.
The lighter the room the less you need worry about a high contrast ratio. If
you were that fussy you would paint your walls black like the cinema.
A few
points to consider before getting carried away with contrast ratio:
The eyes Contrast Sensitivity Function is around 300 for the average person,
it is dependent on the spatial frequency or the gap between parts of the
image that vary in contrast.
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In lower
light conditions i.e. when LUX is halved, a doubling in image area is
required to maintain the same contrast perception which means brighter
images look like they have more contrast and a brighter projector with a
lower CR may seem better than one with less ANSI Lumens (Lower LUX
reading) but has a higher CR, especially in lit conditions. If the light
output from the projector isn't higher than the room average LUX the
image will look washed out as CR will count for little and ANSI Lumens
are king.
-
At low light
levels contrast sensitivity of the eye is approximately 8% of maximum.
Dark adaptation takes 25 minutes to reach 80 percent adaptation, an hour
for full adaptation. (In other words the first hour of the movie is not
your best in this CR battle) This is why pilots (thinking of single
engine light aircraft..) use red torches when flying of a night so in
case of an emergency landing they have a chance too see where they are
landing. Looking at a bright white light kills your night vision. So
looking at a bright scene in a movie doesn't help your eyes sensitivity
to the next dark one! (Can you see where I'm going with this yet?)
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You can get
a much better score or contrast perception by looking at static test
patterns however as home cinema is normally of moving pictures this too
can be misleading.
-
Don't
confuse dynamic range with contrast sensitivity, the eye has the highest
dynamic range around better than any electronic gadget under ideal
conditions you can see in bright sun light or moon light once your eyes
adjust. Most digital cameras are useless in starlight.
-
This doesn't
mean that a projector with a CR of 2000:1 or more isn't better than one
rated at 400:1 however the perceived advantage is a lot smaller than
optimistic claims the manufacturers would have you believe. Note you
must be viewing under ideal conditions to see the largest variance in
contrast.
Some Helpfull notes on contrast:
1. Your Notebook PC is about 300:1 too.
2. Cinema is 1000:1
3. Any light in the room makes higher than say 400:1 contrast ratio
academic.
4. The loss of contrast sensitivity accelerates with age, at 60, the amount
of light reaching the photoreceptors is only 33% of the amount seen at age
20. By the late seventies, the amount falls to 12%.
So what are we saying here?
Don't get all carried away with big contrast ratio numbers, your eye is the
limiting factor, that and the amount of ambient light in the room. We
haven't even touched on the source material.
The size of your projection room (how close the walls and ceiling are to the
screen) plus the paint colour, carpets and fittings can change the ACTUAL
contract ratio by at least a factor of five! I haven't yet seen a Home
Theater room that didn't decrease the actual contrast ratio due to reflected
light. Black walls, carpets and all.
More. . .
-
Aging eyes need more light, especially
for low contrast tasks.
-
Aging eyes are more sensitive to glare.
-
Aging eyes function better with high
contrast for many tasks, like reading.
-
Aging eyes need better lighting
uniformity (but only if there is adequate contrast!).
Peripheral vision may diminish.
-
Changing the eye's focus from one
distance to another is more difficult.
-
Aging eyes respond well to reduced visual
clutter and confusion.
-
As one ages, experiencing a more natural
day/night cycle becomes increasingly important.
In our opinion 2000:1 is fine for light controlled rooms and 400:1 for your
family/living room or presentations.
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