Find Next Point Transition
Find Next Point Transition
Point transitions provide DigImage with a method of encoding (optically) on
the video tape certain events, such as the start of an experiment, in a
manner which may later be picked up automatically. A typical setup might
consist of a light emitting diode (LED) somewhere in the field of view of
the video camera. At the start of each experiment the LED would be flashed
for two or three video fields (an incandenscent lamp is not suitable due to
the relatively gradual turn on and off). Later, when the experiments are
being analysed, use of this option will enable DigImage to automatically
synchronise the VTR with the exact point at which the LED was flashed, thus
enabling a whole series of experiments to be processed without the need for
the user to perform any manual synchronisation between the video tape and
DigImage.
Specify transition point using which buffer ?
The location of the point at which the transition occurs must be specified.
The most convenient method of doing this is to capture one image in which
the point of the transition (eg. the LED) is known, and use this image in
conjunction with the DigImage cursor to specify the coordinates of the
point. Assuming such an image already exists, this entry is used to specify
the buffer in which it is contained.
Cursor Positioning: Location transition point
The DigImage cursor is used to specify the location of the point at which
the transition will occur. If running this feature from a command file,
then the Manual coordinate option should be used to fix the cursor
location. For more details on the use and operation of the cursor, see the
H Help option in the cursor submenu.
Transition threshold ?
The transition is specified by three quantities: the location, the
threshold through which the transition occurs, and the direction of the
transition. This entry specifies the transition threshold. This threshold
should be chosen such that the required feature (eg. flashing LED) produces
a clear, unambiguous, well defined change in intensity from below (above)
to above (below) the threshold. The theshold should be sufficiently
distinct from the limiting intensity values so that noise is unable to
produce any erroneous transitions.
Intensity Increase or Decrease ?
The final part of the transition specification involves specifying whether
the transition is defined on an increasing (I) or decreasing (D) intensity
at the specified point.
Parent menu
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DigImage User Documentation
Stuart Dalziel,
last page update: 19 February 1996