Common Problems in Setting Video Levels
- Threshold too high - the experiment object disappears from view.
- Threshold too low - objects in the cameras' field-of-view, other than the object
you wish to track, exceed the threshold level; data can look "spiky" because the
detection circuitry shifts from the object you want to track to the distracting object.
- Interfering objects in the field-of-view - if your graphs seem to be "spiky" or form
a line, you may have an interfering object whose level is too close to that of the
object you are tracking.
This can easily happen if the interferring object is far away from the experiment area. Observing the Scan Line View or Object View usually helps to locate the object. IF it does not, perhaps the interfering object is in the same horizontal row as the object you are trying to track. To check for this possibility, move your target object to a different height or remove it from the experiment area.
- Video camera exposure is set too high - as with interfering objects, if your graphs seem to be "spiky" or form a line, the video may be saturated in various places causing color artifacts. Some video cameras show saturated areas with striped lines.
- Less than ideal lighting conditions - the automatic gain on most video cameras adjusts
to low-light levels. Sometimes, however, under fluorescent lights that produce very
little red, it may be hard to get good data. In this case, add incandescent clamp
lights to shine on the red objects.
- Camera(s) set to "progressive scan" mode - progressive scan mode takes a new image
only thirty times per second rather than the normal sixty times per second. This
option can cause problems with Motion Visualizer 3D video levels and should be disabled.
- Camera(s) set to output status information - Some video cameras include status information, such as date/time, in their video output. Status information can interfere with obtaining a clean video signal so this option should be disabled. You can check this by viewing the cameras' video output on an external monitor.
Video cameras set themselves to an average level, via an "automatic gain control", which may result in some areas being beyond the dynamic range of the cameras. This is best for a picture, but for our purposes, it is best not to have any saturation in a field-of-view. If your viewfinder, for example, shows white in the middle of a red object, it has probably reached saturation and the exposure should be turned down. Find the "exposure control" setting, and set it for a shorter exposure (the viewfinder should look darker afterwards).