Polycom VSX 7000s Series, Справочное руководство интегратора

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Integrator’s Reference Manual for the VSX Series
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Video Projection for Use in Videoconference
Many installations make use of video projection devices. The most important
thing to remember in the planning of video projection for a videoconference
space is that front projection is vastly inferior to rear projection. Front
projection systems are less expensive and easier to implement, but the
conflicting interest between the camera and the projection display makes this
form of display a very poor choice. Front projection setups operate best when
the lighting in the room is dimmed or doused. When this is done, the
videoconference cameras can no longer operate, since they require even,
bright, color-corrected light. A direct conflict between these two technologies
is clear. In the event that a rear projection room cannot be set aside,
retro-projection units can be purchased from a number of manufacturers.
These units normally are available in sizes ranging from 40” to 72” diagonal
measure. To display high-quality video while maintaining optimum lighting
for interactive video meetings will require a projector of the “light-valve” or
DLP™ class.
Regardless of the exact type of projector selected and the exact nature of “front
versus rear,” there are certain essential rules for projector placement. The goal
in projection is to get the image beam to aim directly into the audience’s eyes.
In Western cultures the average distance from the floor to a seated person’s eye
is 4’. That distance becomes the target for the direct beam of the projector.
Again keep in mind that front projection should be avoided except in the most
extreme cases. If it is employed at all it must be used with an extremely bright
projector (2,500 lumens or greater for any space smaller than 25’x40’).
Cameras
There usually is a “main” or “local people” camera positioned on top center of
the display, so that it can “see” the participants and anything necessary at the
sides of the room, using pan and tilt features. If individual presentations may
be made from the side or “front of audience” area of the room, an additional
camera should be located at the back of the room, also mounted to allow a
view of the presenters when necessary. Some cameras contain an active
camera pointing system that also can be used effectively, given proper care in
the mounting of the camera assembly. The area immediately surrounding the
camera assembly needs to be acoustically “dead” to ensure that the voice
tracking and pointing algorithms work correctly. This is another reason to pay
close attention to the acoustic environment and acoustic treatment of any
space intended for use with this type of camera system.
If local presentation is blended with VC for any events, we must consider the
needs of the presenter who will not be “facing” the local image or inbound
image displays used by the main body of the local audience. One or two
monitors (and a camera) should be mounted at the back of the “audience-end”
of the room, with the horizontal centerline at approximately 5’ from the floor
for ease of presentation interaction between the presenter and the group(s) at
the farend(s). Remember that, with the exception of PC-based information that
is not in a standard composite narrowband video format, any information we