Version 1.0 rev 14 Aug 2019
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The selection of Rolling Shutter or Global Shutter modes depends on your specific experimental conditions. A summary
of the key parameters for each mode is shown in Table 1:
Table 1: Key parameters of Rolling and Global Shutter modes.
Parameter
Rolling Shutter Mode
Global Shutter Mode
Frame rates
Maximum avaliable
Maximum frame rate significantly less than
Rolling Shutter
Read Noise
Lowest
Higher by factor of ~1.4
Spatial distortion
Dependent on object dynamics
None
Rolling Shutter Mode:
with the enhanced frame rates and lower noise, is likely to suit the majority of scientific
applications. As long as the frame rate is such that the camera is temporally oversampling object dynamics within
the image area, negligible spatial distortion will be observed. Such oversampling is good imaging practice, since it is
undesirable to have an object travel a significant distance during a single exposure.
Global Shutter Mode:
with its simpler readout scheme, to both understand and use (no skewed row exposures, easy to
sync with light sources), Global Shutter will be the mode of choice for many users. Global Shutter will have a higher read
noise and lower frame rate compared to Rolling Shutter. Some specific applications for which Global Shutter will be a
necessity are shown in Section 4.5.4. Refer also to Andor Technical Note,
4.5.4 e
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Applications that require exact time correlation between two (or more) points of an image that are separated
vertically within the image:
In Rolling Shutter it takes 18 μs per row for the readout front to move across the
image from the bottom upwards, reading out one row at a time. That means an object at the bottom of the
image will begin and end an exposure ~18.5 ms before an object located at the very top (although remember
that each object will be subject to the same overall exposure time). If a particular application requires that
‘moving or changing’ objects separated by relatively large distances (vertically) be subject to the same
beginning and end of exposure, then Global Shutter mode is required.
•
Applications were every point in the image must be logged accurately (down to nanosecond accuracy)
relative to a GPS timestamp.
In Global Shutter all pixels start the exposure simultaneously and all pixels end
the exposure simultaneously.
•
Applications where relatively large objects in the image field are moving fast (relative to a Rolling Shutter
readout sweep).
Rolling Shutter can sometimes create distortion effects under such circumstances, making
Global Shutter a good option.
•
Applications that require ‘microsecond’ time gating synced to a pulsed light source: e.g. Laser Induced
Breakdown Spectroscopy (LIBS).
Global readout involves a step that simultaneously transfers the signal
charge of each pixel into the corresponding readout node for that pixel. This transfer step is 80 μs, facilitating
fast exposure end, i.e. ‘Electronic gating’
•
‘Double Exposure’ applications:
e.g. Particle Imaging Velocimetry (PIV), which requires that two back-to-back
exposures are acquired with minimal time separation between them. The Global Shutter 80 μs transfer time into
the readout node defines the minimum time between two consecutive exposures
