PPT cameras track infrared (IR) light emitted from PPT markers. Infrared
light from non-marker sources renders tracking unreliable or impossible. Thus,
the tracked workspace should be lit by "cool" light sources (such as fluorescent
or xenon lights) that do not generate IR light.
Common infrared contamination sources
- Windows: Completely block outdoor light from
the room's windows. Standard curtains and venetian blinds are usually not
sufficient as they let through too much IR light. Use a high-quality block-out
plastic or felt drape to achieve full light blockage.
- Incandescent (tungsten) light bulbs: Turn off
all warm light sources and only use fluorescent light to illuminate your
workspace during tracking.
- Some
computer monitors and status lights: Some computer monitors and status
lights on electronic devices emit IR. Use the large camera view when
troubleshooting for interfering light sources.
- Reflective surfaces: Sometimes a surface
reflects a warm light source that would otherwise not be in the field of view of
the PPT cameras (e.g., a ceiling light reflecting off a chrome chair). Even the
glass surface of a widescreen TV or the enamel surface of a white-board can be
reflective enough to interfere.
Light leaking into your workspace?
If tracking is poor or calibration fails, check for light contamination:
- Turn off all of your PPT markers.
- Look at each camera's 2D view. If any show a cross-hair, then there
is stray light.
- Often it is a good idea to raise a camera's sensitivity to better
detect stray light of this sort (lowering sensitivity after the problem light
has been resolved).
Always control ambient lighting?
Yes, every time you use your PPT system you will need to eliminate infrared
light contamination. This includes during calibration and normal tracking. |