Understanding Electronic Camera Shutter Types

Discover the differences between Global Shutter and Rolling Shutter Cameras and gain valuable guidance for selecting the ideal option for your camera-centric application. This comprehensive guide offers a thorough exploration of these sensor types, shedding light on their advantages and disadvantages to empower you with the knowledge needed to make an informed decision.

In the realm of modern industrial cameras and imaging systems, sensors play a vital role in capturing and storing images to cater to diverse processing and analysis requirements. These sensors feature electronic shutters that facilitate image capture. Electronic shutters control the exposure of photon wells within the sensor, determining whether pixels are exposed line-by-line or in a complete matrix. Rolling Shutter and Global Shutter are the two primary variants of electronic shutters. This in-depth article delves into the mechanics of shutter operation, highlights the distinctions between these two types, and provides valuable insights into their specific applications.

To fully grasp the nuanced details discussed in this article, familiarize yourself with the following key terms.

The global shutter mode employed in image sensors offers a remarkable capability where all pixels within the sensor simultaneously start and stop exposing during each image acquisition, precisely following the programmed exposure period. Once the exposure time concludes, the process of pixel data readout commences, progressing row by row until all the pixel data has been retrieved. This distinctive mechanism implemented in global shutter cameras yields undistorted images devoid of any wobble or skewing issues. These global shutter sensors are particularly well-suited for capturing fast-moving objects with exceptional speed.

To provide a better perspective, let’s consider an example of a 640 x 480 resolution image. When this image is exposed using a global shutter, all 307,200 pixels (640 x 480) of the sensor are simultaneously exposed for the designated exposure duration.

It’s important to note that global shutter primarily addresses the avoidance of rolling shutter artefacts, rather than mitigating motion blur caused by rapid movement and exposure. Only at lower exposure levels does the global shutter excel in capturing crisp images of moving objects, eliminating motion blur. Conversely, with a rolling shutter, irrespective of the exposure values used, the resulting images will inevitably exhibit skewing due to the inherent rolling shutter artefact.

In contrast to global shutter cameras, the rolling shutter mode employed in cameras exposes pixel rows sequentially, with a temporal offset between each row. The image capture process begins with the top row, which starts collecting light and completes the exposure before moving on to the next row. This sequential progression introduces a delay in the starting and ending times of light collection for each consecutive row. It’s worth noting that the total light collection time for every row remains consistent.

To provide a better perspective, let’s consider an example of a rolling shutter in a 640 x 480 resolution image. The exposure process begins with the topmost row among the 480 pixel rows and subsequently proceeds row by row in a sequential manner.

The Global Reset Release (GRR) shutter serves as a hybrid between the global shutter and rolling shutter, amalgamating their respective advantages. GRR shutter cameras initiate exposure simultaneously for all sensor pixels, akin to global shutter. However, upon concluding exposure, there exists a temporal offset (tRow) between consecutive rows, akin to rolling shutter.

The tRow values remain consistent with those found in rolling shutter cameras, albeit varying across different camera models.

When utilizing the GRR shutter type, it is imperative to employ flash lighting. Failing to do so can result in significant variations in brightness throughout the acquired images, stemming from differences in exposure times between individual rows. Additionally, capturing images of fast-moving objects may lead to distortions caused by temporal shifts resulting from varying exposure end times among the rows.

To facilitate the use of flash lighting, most cameras are equipped with a Flash Window output signal.

The disparity between a rolling shutter sensor and a global shutter sensor becomes particularly evident in dynamic image acquisition scenarios. When fast-moving objects are captured using a rolling shutter sensor, the occurrence of the rolling shutter effect becomes apparent. Unlike global shutter sensors where all pixels are exposed simultaneously, a rolling shutter sensor scans each row of sensor pixels sequentially. Consequently, if an object moves at a speed that surpasses the exposure and readout time of the image sensor, the resulting image becomes distorted due to the rolling light exposure phenomenon. This phenomenon is commonly referred to as the rolling shutter effect.

Global shutter cameras are widely utilized for capturing high-speed moving objects without encountering artifacts or motion blur. These cameras find extensive application in various domains, including ball tracking, industrial automation, warehouse robots, drones, and live cell imaging. On the other hand, rolling shutter sensors boast exceptional sensitivity, making them suitable for cost-effective applications. They are commonly employed in capturing slow-moving objects like agricultural tractors, slow-speed conveyors, as well as standalone applications such as kiosks and barcode scanners.

Global Shutter technology offers several noteworthy advantages over its counterparts:

Here are the main disadvantages associated with Global Shutter technology:

The prominent advantages of rolling shutter cameras are as following: