Page 101 of 120

Camera modes of operation 101
Long exposure or integration mode
In long exposure or integration mode, the exposure time is controlled internally
via switches on the camera, or externally by way of the frame grabber. In this mode,
an external trigger signal is provided to the frame grabber which, in turn, activates
the camera. In this mode, the signal from the frame grabber to the camera is
referred to as the exposure signal.
Y With most cameras, the exposure pulse is latched to the horizontal synchronization
signal (hsync). The camera uses this horizontal synchronization signal to initiate
frame transfer on its next vertical synchronization signal. In general, the exposure
R time must be specified as a multiple of fields or frames, where one frame time (the
frame transfer time) is equal to the reciprocal of the frame rate of the camera when
A 5 operated in continuous mode. Note that one field time is half of one frame time.
IN 0 ❖ Use long exposure or integration mode when an exposure time greater than one
frame time is required. Most cameras will ignore the end of an exposure pulse that
0 arrives before the current frame period is over, while others will latch to the pulse
and initiate the next exposure directly afterward.
IM 2 To ensure capturing an image:
• If the exposure is internally controlled, the shortest time between external trigger
L Y pulses should be greater than the sum of the exposure pulse width, the exposure
time, and the frame transfer time.
E A • If the exposure is externally controlled, the shortest time between external trigger
pulses should be greater than the sum of the exposure pulse width and the frame
transfer time.
R M ❖ The width of the exposure pulse determines the exposure time and is adjusted
on the frame grabber using Matrox Intellicam or MIL.
P 9The signals used in this mode are an external trigger signal provided to the frame
1grabber, an exposure signal supplied by the frame grabber to the camera, and the
video output (analog and digital) and synchronization signals provided to the
frame grabber.
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