Video and data projection
SXGA
and 16:9 aspect ratios and projection screens
 You
should be aware that you need to think about screen aspect ratio
if you plan to project SXGA computer graphics, wide-screen or
HDTV video. The SXGA standard uses a 5:4 aspect ratio and wide-screen
video a 16:9 ratio, while standard video, VGA, SVGA, XGA and UXGA
use 4:3.
The three
aspect ratios are shown in the drawing at right. Here we've sized
the images so that the width is the same for each, which is the
situation you'd have if you were using a native SXGA projector
and a 5:4 screen. You can see that if you switch to a 4:3 image,
it won't be quite as tall as the 5:4, and the 16:9 image is significantly
shorter.
If, on the
other hand, you start with a native 4:3 aspect-ratio projector
and a standard video-format (4:3) projection screen, then switch
to SXGA, you'll end up with fairly narrow blank areas to the left
and right of the image. (Switching to 16:9, you'll still have
blank strips at the top and bottom of the screen.)
If you start
with a native 16:9 projector and screen, your image will stay
the same height but get progressively narrower when you go to
4:3 and 5:4 images.
There are
two ways to handle this issue.
1. Live
with it. Choose the aspect ratio you will most often use and
buy the screen to match. Da-Lite and Draper now routinely make
5:4 and 16:9 screens, though they are generally special-order.
Some projector
manufacturers are making it easier to live with a single-format
screen. Sharp's newest native SXGA projector, for example, gives
you the ability to resize 4:3 formats to a 5:4 aspect ratio if
you choose, thus making it possible to use a 5:4 screen for almost
everything. Yes the image will be distorted, but the distortion
is slight.
2. Buy
a multi-aspect ratio screen. Da-Lite's motorized Horizon Electrol,
for example, has borders that move to give you up to four different
aspect ratios. You choose what you want and your supplier can
program the screen. You can even set up an AMX or Crestron control
system to automatically change the screen to match the computer
or video source. This is an elegant, if more expensive, way to
handle 4:3, 5:4 and 16:9 aspect ratio sources.
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