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FAQ |
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What is "screen gain" ? |
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Screen gain is the degree of brightness of the image projected on the
screen. A high screen gain |
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indicates a bright screen while low screen gain indicates a dark screen.
Gain is a measure of |
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reflectivity. Screen gain can varies from 0.5 to 12. |
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| What is "viewing angle" ? |
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The viewing angle is the maximum angle at
which the image on the screen can be recognized |
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when a person is viewing the screen from the
side. The viewing angle is expressed in terms of
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both the vertical (up or down) and
horizontal (left or right) angle of the screen. |
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Flatness of the
Projection Screen is very important if you plan to project computer
text, since |
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most projectors have a very narrow plane of
focus and will not provide a consistently sharp image |
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on a rippled screen. Obviously, this will
not be a problem with a rigid rear screen or even with |
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fast- fold, but it is a big factor in a wall
screen. Tensioning systems physically pull a flexible |
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material straight to greatly improve the
image focus. |
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How to choose screen
fabrics surface? |
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You'll need to choose a
surface with your projection source and lighting conditions in mind. It
will |
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determine the sharpness
and brightness of your projected image. In front projection, matte white
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surfaces (by far the most
popular) offer excellent definition for finely-detailed images, such as
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computer text, while
providing very good image. Silver or high gain provide particularly
bright |
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images best foe video or
computer projection. In rear projection situations, there are a variety
of |
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coatings and screen
materials designed for specific situations. Most standard surfaces are
best |
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for rooms with a
relatively narrow seating cone and good lighting control, with specialty
surfaces |
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available when viewing
angles will be wide or lighting high. |
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Comparison between Front
and Rear screen |
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For most purposes, a
front projection screen is the obvious choice, simply because it can fit
into |
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any room without the need
to build a projection booth. Still, a rear screen has advantages. It
will |
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permit the use of visuals
in near normal room lighting, allowing your audience to take notes and
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your speaker to maintain
eye contact with audience members. No matter what your lighting |
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levels, the effects of
ambient light will be reduced, producing images of better contrast.
Speakers |
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may walk in front of a
rear screen without casting shadows. Finally, the noise and distraction
of |
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equipment is eliminated
by moving it to a separate room. |
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Screen Gain and
Directivity |
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Higher screen gain
contributes to higher brightness. However as the screen became higher
the |
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scale of reflected light
directivity becomes narrow. In other words, the viewing angle became
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smaller. Therefore for
deciding which screen to use the correlation between the screen gain and
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directivity should be
considered in addition to the room conditions and the application. |
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What is "resolution" ? |
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The resolution of an
image is the degree to which small details are reproduced. This is
usually |
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expressed in the form of
W x H, where W and H respectively refer to the number of
horizontal |
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and vertical dots that
make up an image. (these dots are also called picture
elements or pixels). |
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The higher the
resolution, the sharper the image. |
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What is "contrast ratio"
? |
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Contrast ratio is ration
between the brightness and darkness sections of an image. A higher
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contrast ratio means a
clearer picture. Rear projectors that are not affected by room lighting
or |
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sunlight have the highest
contrast ratio, so their images are the clearest and easiest to see. |
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What is "keystone
correction" ? |
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Keystone correction on a
tripod or wall screen tilts the top of the screen forward to minimize
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rectangular distortion
caused by the projector being positioned lower than the center of the |
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screen. Tilting the
screen will not always be necessary, as many video projectors have their
own |
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correction built in. It's
important, however, with slide, overhead and many LCD projectors. |
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Why need "black
borders" ? |
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Blacks borders can be
very helpful. They provided a crisp edge for any picture, eliminating
any |
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wash onto the wall behind
your screen and masking any unevenness due to out-of-level |
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projectors. By their
contrast with the projected image, they also fool the eye into
perceiving the |
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image as brighter and
more colorful than it would otherwise be. |
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How does the type of
screen affect brightness ? |
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You should choose the
type of screen based on the location where it will be
used. In general, |
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the larger the
screen the darker the image. However,
you can boost the brightness somewhat |
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by choosing a screen with
a higher gain. Such screens are especially useful for
long and narrow |
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room. If you have a wide
room, then you should choose a screen with a wide viewing angle. |
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