Controlling image capture
MARLIN Technical Manual
V2.4.0
113
Controlling image capture
Shutter modes
The cameras support the SHUTTER_MODES specified in IIDC V1.3. For all mod-
els this shutter is a
global shutter
; meaning that all pixels are exposed to
the light at the same moment and for the same time span.
Continuous mode
In continuous modes the shutter is opened shortly before the vertical reset
happens, thus acting in a frame-synchronous way.
External trigger
Combined with an external trigger, it becomes asynchronous in the sense
that it occurs whenever the external trigger occurs. Individual images are
recorded when an external trigger impulse is present. This ensures that even
fast moving objects can be grabbed with no image lag and with minimal
image blur.
Camera I/O
The external trigger is fed as a TTL signal through Pin 4 of the camera I/O
connector.
CMOS sensors
For CMOS sensors, a global shutter is not common. Normally a rolling curtain
shutter is used to shorten the exposure or integration time. The curtain's
width defines the integration time and the curtain sweeps with the frame
readout time over the image. Although this is appropriate for still images,
image distortion will be created with moving objects, because the upper
image part is scanned earlier than the lower image part. For this reason the
MARLIN F-131 features a non pipelined global shutter only. A side effect of
this type of global shutter is that the integration or shutter time is added to
the readout time, thus affecting the frame rates to be achieved.
Trigger modi
Marlin cameras support IIDC conforming Trigger_Mode_0 and
Trigger_Mode_1 and special Trigger_Mode_15 (bulk trigger).
Trigger Mode
also known as
Description
Trigger_Mode_0
Edge mode
Sets the shutter time according to the value set in
the
shutter
(or extended shutter)
register
Trigger_Mode_1
Level mode
Sets the shutter time according to the
active low
time
of the pulse applied (or active high time in
the case of an inverting input)
Trigger_Mode_15
Programmable mode
Is a
bulk
trigger
, combining one external trigger
event with continuous or one-shot or multi-shot
internal trigger
Table 37: Trigger modi