User`s manual

1.5 Global Shutter

The STOC has a global shutter. 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 STOC 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 1-2 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

STOC has simultaneous exposure and readout, that is, while the pixels are

being exposed, the previous image is being read out.

Figure 1-2 Sequence taken by the MT9V022. Exposure 0.7 ms, 30 Hz, 640x480 video stream. Sequence shows about every 4

frame.