How To Choose: Global Shutter V.s. Electronics Rolling Shutter Cameras

Introduction

From smart-phones to industrial imaging systems, cameras are found everywhere. Modern digital cameras use electronic shutters for capturing images. The purpose of a camera shutter is to control the exposure time. It consists of a movable barrier that can be opened and closed to allow light to pass through the lens and expose the image sensor. An important feature of the sensor is its shutter type. The two main types of electronic shutters are global shutters and rolling shutters. These shutter types differ in their operation and final imaging results, especially when the camera or target is in motion.

What is global shutter?

Global shutter is a type of camera shutter that exposes all pixels of an image sensor simultaneously, rather than exposing each row of pixels one at a time. This means that when a global shutter camera takes a picture, all parts of the image are captured at the same instant, resulting in a clear, undistorted image with no motion blur or distortion. Global shutters are often used in applications where fast moving subjects or fast panning are present, as they are able to capture these movements without distortion. They are also useful in environments with high levels of vibration, as they are less susceptible to image distortion caused by camera movement. Global shutters are typically found in high-end digital cameras and some specialized cameras such as those used in scientific or industrial applications.

What is rolling shutter?

Rolling shutter is a type of camera shutter that exposes each row of pixels on an image sensor sequentially, rather than exposing all pixels simultaneously like a global shutter. This means that when a rolling shutter camera takes a picture, different parts of the image are captured at slightly different times. This can result in image distortion, especially when the camera is moving or when there are fast-moving objects present in the scene.

One common example of rolling shutter distortion is the “warping” effect that can occur when panning a camera quickly. The top and bottom of the image may appear to be skewed or stretched, while the middle of the image remains relatively unchanged. This distortion can also occur when an object moves very quickly through the frame, causing it to appear elongated or distorted.

Rolling shutter cameras are generally less expensive than global shutter cameras and are more common in consumer-grade digital cameras and smart-phones. They are generally less sensitive to motion blur than global shutters, but may produce distorted images in certain situations.

How global shutter works?

As described earlier, a global shutter camera captures an image by exposing all the pixels in the image sensor simultaneously, rather than scanning the image sensor line by line as in a rolling shutter camera. This allows the entire image to be captured at the same instant in time, which can be important in certain applications where fast-moving objects or high-speed events are being captured.

One way that a global shutter camera can achieve this is by using a charge-coupled device (CCD) image sensor. CCD sensors are made up of a grid of photodiodes, which convert light into electrical charges. When an image is captured, the charges are transferred from the photodiodes to a storage area within the CCD, and then read out all at once when the exposure is complete.

Another way to achieve a global shutter is through the use of a complementary metal-oxide-semiconductor (CMOS) image sensor with a global shutter feature. In this case, the CMOS sensor is divided into a series of tiny photodiodes, each of which is paired with a transistor that can hold a charge. When an image is captured, the transistors are used to hold the charges from the photodiodes until the exposure is complete, at which point the charges are transferred to a storage area and read out all at once.

How rolling shutter works?

A rolling shutter camera captures an image by scanning the image sensor line by line, rather than exposing all the pixels simultaneously as in a global shutter camera. This means that each row of pixels is exposed to light source at a slightly different time, resulting in a rolling effect as the image is captured.

In a rolling shutter camera, the image sensor is typically made up of a grid of photodiodes, which convert light into electrical charges. When an image is captured, the charges from the photodiodes are transferred to a storage area within the image sensor and then read out line by line. This process can take a finite amount of time, and as the image is being read out, the camera continues to expose the remaining rows of pixels to light.

Pros and cons of global shutter and rolling shutter

Pros and cons of global shutter

Some of the major advantages of global shutter include:

1. Better image quality: Global shutter cameras capture the entire image at the same time, which can result in higher image quality compared to rolling shutter cameras.
2. Less distortion of fast-moving objects: Because the entire image is captured at the same time, global shutter cameras are less likely to produce distortions in images of fast-moving objects compared to rolling shutter cameras.
3. Ability to capture high-speed events: Global shutter cameras can capture high-speed events with greater accuracy, as the entire image is captured at the same time.

The main disadvantages of global shutter are as following:

1. Cost: Global shutter cameras can be more expensive than rolling shutter cameras.
2. Longer readout times: The process of reading out the charges from the image sensor in a global shutter camera can take longer than in a rolling shutter camera. This can limit their use in certain applications where high frame rates are required.
3. Limited availability: Global shutter cameras are not as widely available as rolling shutter cameras.
4. Lower light sensitivity: Global shutter cameras may have lower light sensitivity compared to rolling shutter cameras, which can limit their use in low light conditions.

Pros and cons of rolling shutter

Some of the salient advantages of rolling shutter are as following:

1. Cost: Rolling shutter cameras are typically cheaper and more widely available than global shutter cameras.
2. Faster readout times: The process of reading out the charges from the image sensor in a rolling shutter camera is generally faster than in a global shutter camera, which can make them more suitable for certain applications where high frame rates are required.
3. Energy efficiency: Rolling shutter cameras can be more energy efficient and have lower power requirements than global shutter cameras.

The main disadvantages of rolling shutter are as following:

1. Image quality: Rolling shutter cameras may produce lower image quality compared to global shutter cameras.
2. Distortion of fast-moving objects: Rolling shutter cameras can produce distortions in images of fast-moving objects, as the image of the object is captured at different time across the image sensor. This can lead to the object appearing skewed or stretched in the final image.
3. Difficulty capturing high-speed events: Rolling shutter cameras may have difficulty capturing high-speed events accurately, as the image may be captured over a longer period of time than in a global shutter camera.
4. Limited use in certain applications: The disadvantages of rolling shutter cameras may limit their use in certain applications, such as scientific imaging or high shutter speed photography.

Conclusion

In this article we have discussed the two main types of camera shutters i.e global and rolling shutters. Global shutter exposes all the pixels of the image sensor simultaneously while the rolling shutter exposes rows of pixels in a sequential manner. Global shutters offer the advantages of better image quality, low distortion, and capturing of high-speed events. Rolling shutter cameras, on the other hand, offer the advantages of low cost and fast read-out times. Global shutter cameras are more suitable for high-end specialized applications while rolling shutter cameras largely cater to the needs of the masses.