Introduction to Practical Applications
The pseudo-global shutter technique, enabled by hardware triggering, has
proven invaluable in a wide range of scientific imaging applications. This article
explores the practical implementation of pseudo-global shutter operation, with
particular emphasis on multi-channel imaging—one of the most common
applications in microscopy. The ability to effectively transform a rolling shutter
camera into a device that behaves like a global shutter camera opens up new
possibilities for researchers working with CMOS sensors. Understanding the
rolling shutter in camera systems is fundamental to appreciating the benefits
of this technique.
Multi-Channel Imaging and the Rolling Shutter Challenge
Multi-channel imaging, where multiple wavelength channels, polarization
channels, z-positions, and/or x/y stage positions are acquired for a single
dataset, is extremely common in microscopy. However, the rolling shutter
CMOS camera, which is the most common type of camera used in microscopy,
presents significant drawbacks for this type of imaging without the use of
hardware triggering.
As rolling shutter cameras can overlap the acquisition of subsequent frames,
any hardware changes that occur between frames can happen while exposure
is still taking place. Software typically does not account for the duration of the
rolling shutter finishing the exposure, leading to artifacts. For example, in
red/green alternating wavelength acquisition, part of the image captured with
red emission light may actually be captured when the camera is intending to
capture green emission light, and vice versa. This cross-over between channels
compromises data quality and can lead to incorrect experimental conclusions.
Understanding the rolling shutter in camera systems is therefore critical for
researchers performing multi-channel imaging. The Tucsen Dhyana 400BSI v3,
like many modern scientific cameras, offers features that help address these
challenges. The rolling shutter in camera designs inherently creates these
timing challenges, making pseudo-global techniques particularly valuable.
Light Efficiency Considerations
For experiments where light efficiency is a critical factor—such as biological
imaging where the goal is to minimize photobleaching or phototoxicity—there
is an additional efficiency consideration when using rolling shutter cameras
without triggering. During both the period when the rolling shutter is starting
exposure and when it is stopping exposure, on average only half of the rows of
the camera are exposing to light. When combined with the poor timing
precision of software-controlled light source activation, this leads to
significantly reduced light efficiency compared to what would be achievable
with hardware-triggered control. The rolling shutter in camera systems thus
imposes fundamental limitations on light efficiency that can only be overcome
through triggering techniques.
Solutions to the Rolling Shutter Challenge
There are two possible solutions to these issues. The first approach involves
using software or hardware to introduce a delay to all hardware movements
after camera acquisition to account for the rolling shutter. However, due to the
low precision of software timing, adding a sufficiently long delay to be
foolproof is likely to add significantly to the overall experiment duration. For
most multi-channel imaging applications, this is highly undesirable.
The second solution is using cameras with a pseudo-global triggering output,
as is the case for most high-end rolling shutter sCMOS cameras. The Tucsen
Dhyana 400BSI v3 is an example of a camera that offers this capability. If this
trigger is used to activate the light source, the light source will only activate
when all of the rows of the camera are exposing. This approach maximizes light
efficiency and ensures that there is no overlap between the exposure of frames.
By leveraging the rolling shutter in camera systems in this way, researchers can
achieve results that were previously difficult to obtain with rolling shutter
sensors.
If hardware changes such as changes to illumination wavelength are also
triggered to begin when the trigger signal goes low, the hardware changes and
the rolling of the camera shutter can begin simultaneously, maximizing time
efficiency. Depending on the complexity of the hardware setup, managing the
triggering of multi-channel experiments may require a DAQ card or other
experimental controller. The rolling shutter in camera designs can be effectively
managed through these triggering strategies, as demonstrated by cameras like
the Tucsen Dhyana 400BSI v3.
Benefits of Pseudo-Global Shutter Operation
The benefits of pseudo-global shutter operation are substantial. By effectively
emulating the behavior of a global shutter camera, this technique eliminates
the artifacts and inefficiencies associated with the rolling shutter. Light
efficiency is maximized, as illumination is only active during the period when all
rows are simultaneously exposing. Cross-talk between channels in
multi-channel imaging is eliminated, as there is no overlap between the
exposure of successive frames. Timing precision is dramatically improved
through the use of hardware triggering, which provides microsecond latency
and consistent performance independent of computer workload.
The rolling shutter mechanism need not be a limitation in scientific imaging
when pseudo-global shutter techniques are properly implemented. By
combining a camera with pseudo-global trigger output capabilities—such as
the Tucsen Dhyana 400BSI v3—with a high-speed triggerable light source and
appropriate triggering configuration, researchers can achieve results that rival
those of true global shutter systems. Understanding the rolling shutter in
camera systems and its limitations is the key to unlocking the full potential of
these techniques.
Summary of Pseudo-Global Shutter Applications
| Application | Challenge | Pseudo-Global Shutter Solution |
|---|---|---|
| Multi-Channel Imaging | Cross-talk between channels | Illumination only during all-rows-exposing period |
| Live-Cell Imaging | Photobleaching, phototoxicity | Maximized light efficiency reduces sample damage |
| High-Speed Imaging | Timing artifacts | Microsecond precision via hardware triggering |
| Hardware Coordination | Movement during exposure | Triggered synchronization with stages, filter wheels |
Summary of Key Principles
In conclusion, pseudo-global shutter operation represents a powerful
technique for overcoming the inherent limitations of rolling shutter CMOS
cameras in scientific imaging. By using hardware triggering to coordinate
camera exposure with illumination, researchers can effectively transform their
rolling shutter cameras into devices that behave like global shutter cameras.
This technique eliminates artifacts, maximizes light efficiency, and enables
precise synchronization with other hardware components. Whether applied to
multi-channel imaging, live-cell microscopy, or high-speed experiments,
pseudo-global shutter operation offers a practical and effective solution for
researchers seeking to get the most out of their CMOS cameras. Models like
the Tucsen Dhyana 400BSI v3 demonstrate how modern scientific cameras are
designed to support these advanced triggering techniques, making them
valuable tools for the research community. The rolling shutter in camera
systems continues to evolve, and techniques like pseudo-global operation
ensure that these cameras remain highly capable for a wide range of
applications.
