Baumer EXG03 - Page 7

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2.1.1.1 GlobalShutter
Pixel
Active Area (Photodiode)
Storage Area
Microlens
Global shutter means that all pixels of the sensor are reset and afterwards exposed for a
specied interval (t
exposure
).
For each pixel an adjacent storage area exists. Once the exposure time elapsed, the
information of a pixel is transferred immediately to its storage area and read out from
there.
Due to the fact that photosensitive surface get's "lost" by the implementation of the stor-
age area, the pixels mostly are equipped with microlenses, which focus the light to the
pixels active area.
2.1.1.2 RollingShutter
Reset Pointer
Readout Pointer
Pixels of Frame
(n-1)
– will be deleted
Currently exposed pixels (Frame
(n)
)
Read out pixels of current Frame (Frame
(n)
)
Rolling shutter means that – in contrast to the global shutter – not the whole sensor is
exposed at once, but single portions successively. It is said the shutter "rolls" over the
sensor�
For Baumer EXG cameras with rolling shutter this means two pointers are "rolling" across
the sensor:
▪ First, the reset pointer deletes any information of former exposures stored within the
pixels (Frame
(n-1)
). After that the pixels are empty and restart collecting information
from incoming light – the new exposure (Frame
(n)
) begins.
▪ Once a predened interval – the exposure time t
exposure
– is elapsed, the readout
pointer rolls across the sensor and the information of the pixels is read out.
▪ For example: On Baumer EXG50, the pass of a pointer lasts approx. 72 msec
(t
Full Frame
).
Notice
Due to technical issues of rolling shutter, a ash control depending on the exposure
time does not make sense. Such cameras should be used in a continuously illuminated
environment.
◄Figure5
Structure of an imaging
sensor with global shut-
ter (interline).
◄Figure6
Operating mode of a
rolling shutter.