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APPENDIX A. GLOSSARY
PAGE 44
10
Operating (Exposure) Modes
The PL-A741 has two shutter types:
•
Rolling Shutter (free-running image capture)—See Section 10.2, below
•
Synchronous Shutter (triggered image capture)—See Section 10.3, on page 45
Table 10.1 Capture Methods
Use of Other Sync.
Device Possible?**
(e.g., Strobe, Flash)
Method
Capture Type
Shutter
Type
Free-Running Continuous
Continuous
Rolling
No
Internally Triggered Free-Running
Continuous
Continuous
Synchronous
No
Hardware Triggered Frame-onDemand
Frame-on-Demand
Synchronous
Yes
Software Triggered Frame-onDemand
Frame-on-Demand
Synchronous
Yes
** This applies only to the use of the camera with the PixeLINK API or PixeLINK software.
10.2 Rolling Shutter
With a Rolling Shutter, only a few rows of pixels are exposed at one time. The camera
builds a frame by reading out the most exposed row of pixels (and ceasing exposure of
that row), starting exposure of the next unexposed row down in the Region of Interest
(ROI; the user-specified active area on the imager), then repeating the process on the
next most exposed row and continuing until the frame is complete. After the bottom row
of the ROI starts its exposure, the process “rolls” to the top row of the ROI to begin
exposure of the next frame’s pixels.
The exposure down each frame, and from frame-to-frame, remains consistent due to this
continuous read-out.
The row read-out rate is constant, so the longer the exposure setting, the greater the
number of rows being exposed, or integrated, at a given time. (“Integrated” means
that the pixels are building up, or integrating, an electrical charge in response to the
photons hitting them.) Rows are added to the exposed area one at a time. The more
time that a row spends being integrated, the greater the electrical charge built up in the
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PixeLINK PL-A741
Machine Vision Camera
System Guide