In machine vision systems the sensor is the heart of the camera. Responsible for much of the image capture responsibilities, image sensors come in many different forms. Broadly speaking, most image sensors are either Charged Coupled Device (CCD) or complementary metal-oxide-semiconductor (CMOS) sensors. Each type of sensor uses either a rolling shutter or a global shutter.
The shutter controls the way the camera is exposed to a scene and how the charges built up in the pixel are read out. Rolling shutters and global shutters both control exposure, but complete pixel readout in different ways.
How are Rolling Shutters and Global Shutters in Image Sensors Different?
The primary difference between these two types of shutters is in the speed of pixel readout. In a rolling shutter, for example, the readout wave travels from the center of the sensor to the top, and from the center of the sensor to the bottom, in two different readouts. The result is a slight delay in exposure time for the top and bottom of the sensor compared to the middle, which inherently limits the speed of the sensor.
Global shutters are a newer technology. They expose all pixels to an image at the same time and pixel readout occurs simultaneously, which eliminates any delay in exposure times like in rolling shutters. However, simultaneous exposure comes at the cost of higher read-out noise levels. Both rolling shutters and global shutters have advantages and disadvantages.
When is Each Type of Shutter Used in the Industrial Sector?
Rolling shutters, as mentioned, are inherently limited in terms of speed. They’re not often used in imaging applications where fast-moving objects need to be captured. Rolling shutters are most useful for ultra-high resolution sensors where the readout noise from global shutters would be too impactful on image quality.
Global shutters, on the other hand, are widely used in the industrial sector for high-speed imaging. Since the simultaneous exposure and readout doesn’t create image distortion when capturing fast-moving objects, global shutters are perfect for these applications, especially when slightly higher levels of readout noise won’t impact the accuracy or reliability of imaging.
Both rolling shutters and global shutters have their niche applications in the industrial sector. Rolling shutters are better equipped for high resolution, and global shutters are better equipped for high speeds.
While both types of shutters control exposure and pixel readout in cameras, they do so in very different ways. Rolling shutters and global shutters play a major role in the performance of a machine vision system.
To learn more on this topic, browse rolling shutter and global shutter sensors from Phase 1 Technology.