Polycom 2457-26122-001 ユーザーズマニュアル

 Integrator’s Reference Manual for the Polycom RealPresence Group Series

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Polycom, Inc.

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’).

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