SVS-Vistek HR Series, Manual

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SVS-VISTEK
Feature description 18
6 Feature description
This chapter covers features of SVCam cameras. Not every feature might
be supported by your specific camera model. For information about the
features of your specific model, please refer to the specifications area with
your exact model.
6.1 Basic Understanding
6.1.1 Global shutter
The shutter is describing the functionality of exposing the light sensitive
pixels of the sensor to light for a limited time. With global shutter all pixels
are exposed to light at the same time for the same time.
All pixel will be exposed to light at the same starting point, and all pixel
light exposure will stop at the same time. Fast moving objects will be
captured without showing movement distortion, except motion blur if the
moving object is so fast that the same point of the object covers different
pixels at start and end while exposing.
Using flash with global shutter is straight forward: just make sure your
flash is on while shutter is open, thus all pixels are exposed to light the
same time. You might flash at any time within exposure time.
6.1.2 Rolling Shutter
Rolling shutter is a method of reading out a CMOS sensor, where the
whole scene is scanned line after line very rapidly. Rolling shutter cameras
in general are more sensitive in their light response than global shutter
ones.
Despite the speed of scanning one line after the other („rolling“) is very
high, it is important to note that the instant of imaging a single line will be
different to the point of time of the next line imaging. As this works out
without any effect in the final image with still sceneries, with moving
objects you get geometric distortions (see example of rotating propeller),
showing fast moving structures in an predictable, in the first moment yet
surprising way.
As it takes some time to read out a whole sensor (and the whole sensor
has always to be read out!) you need to make sure that light conditions
are stable while reading the sensor. This restriction applies especially to
using PWM driven lights or flash lighting with rolling shutter. Unstable
light conditions will result in a horizontal line structured pattern noise.
propeller w/ rolling shutter artifacts