STH-DCSG
U
SER
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S
M
ANUAL
©
2005
V
IDERE
D
ESIGN
5
1.2 Global
Shutter
The STH-DCSG has a global shutter (the “G” designation in STH-DCSG).
Almost all other CMOS imagers have a
rolling
shutter. With rolling
shutter, each row of pixels is exposed just before it is read out. So each row
is exposed at a different time from other rows. This leads to
motion blur
–
a skewing of moving objects from top to bottom.
Global shutter, on the other hand, exposes every pixel at the same time.
The charge on exposed pixels is then transferred to a set of storage bins,
and read out to give an image. Because the pixels are exposed at the same
time, there is no motion blur. With its high sensitivity, the STH-DCSG
allows for very short exposure times, even under moderate lighting
conditions. So it is appropriate for high-motion applications, such as
outdoor robotics, motion capture, etc. Figure 1-1 shows an example of
motion capture using the device. Notice the stop-action motion of the
model plane.
Although there are a small number of global-shutter CMOS imagers, most
of them are
sequential
, that is, the pixels are exposed, then read out. The
pixels cannot be exposed again until readout finishes. With sequential
readout, either the framerate or the maximum exposure is limited. The
STH-DCSG has
simultaneous
exposure and readout, that is, while the
pixels are being exposed, the previous image is being read out.
Figure 1-1 Sequence taken by the MT9V022. Exposure 0.7 ms, 30 Hz, 640x480 video stream. Sequence shows about every 4
th
frame.
