Nano Series GigE Vision Camera On-Semi Sensor Models • 87
Guide to Using a Rolling Shutter Camera
The Genie Nano C4900 implements the On-Semi AR1820HS rolling shutter sensor to achieve a high
pixel density low cost solution for a number of imaging implementations. These sensors have
different usage characteristics and thus provide different application solutions compared to the
Nano global shutter models. The following points highlight those differences:
Simpler Sensor Design Attributes
• Rolling shutter cameras have a simpler design with smaller pixels, allowing higher
resolutions for a given sensor physical area. As an example, mobile phones use rolling
shutter sensors.
• Depending on the imaging requirements, the higher density pixel array may require a
higher quality lens. Lens specifications define the Resolution and Contrast/Modulation
attributes which must be considered. This commonly used gauge is the Modulation Transfer
Function (MTF) which is extensively covered by lens suppliers to qualify their products.
Consider reading https://www.edmundoptics.com/resources/application-
notes/optics/introduction-to-modulation-transfer-function/ as an initial start to
understanding MTF.
• A rolling shutter sensor exposes, samples, and reads out sequentially, as part of the design
criteria to achieve a higher pixel density via simplified circuitry.
• Rolling shutter sensors generate less heat which translates to a lower noise level (SNR).
• Global shutter CMOS sensors require a more complicated circuit architecture, thus limiting
the pixel density for a given physical size.
Rolling Shutter Trade-offs
When selecting a rolling shutter camera, the user needs to understand that the camera is not
suitable for all machine vision applications. Examples of limitations are:
• A rolling shutter camera is unsuitable for applications like barcode scanning, machine vision,
or automated inspection systems, which require the imaging of rapidly moving objects.
• Moving objects are subject to temporal distortions best described as positional errors
(shifts) from the top of an object to its bottom, due to how individual lines are exposed
(detailed below).
• Rolling shutter cameras using Global Reset Release mode (GRR) are not suitable for moving
objects in well-lit environments.
• Degree of distortions change as exposure time is increased or decreased.
• Use of a strobe flash with a controlled duration, in a dark imaging environment, is required
to eliminate positional distortions.
• The Internet has many sources and examples of the visual distortions due to Rolling Shutter
sensors, mostly in reference to using cell phones and consumer cameras.
(e.g. https://www.youtube.com/watch?v=dNVtMmLlnoE “Rolling Shutter Explained”)
The guidelines that follow will permit the successful usage of rolling shutter cameras in
machine vison applications.
Guide to ERS or GRR Exposure Modes.
The following two pages provide overviews and constraints on using either the typical Electronic
Rolling Shutter (ERS) Exposures or Global Reset Release (GRR) Exposures modes.
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