The difference between global shutter and rolling shutter
August 9, 2021
What is a shutter？
The shutter is a mechanism used by the camera to control the effective exposure time of the photosensitive film. It is an important part of the camera, and its structure, form and function are an important factor to measure the quality of the camera.
What is Global Shutter ?
This is achieved by exposing the entire scene at the same time. All pixels of the Sensor collect light at the same time and expose at the same time. That is, at the beginning of the exposure, the Sensor starts to collect light; at the end of the exposure, the light collection circuit is cut off. Then the Sensor value is read out as a picture. CCD is the working method of global shutter. All pixels are exposed at the same time.
What is Rolling Shutter?
Unlike the Global shutter, it is achieved by the Sensor's progressive exposure method. At the beginning of the exposure, the Sensor scans line by line and performs exposure line by line until all pixels are exposed. Of course, all actions are completed in a very short time. The exposure time of pixels in different rows is different.
Global shutter exposure time is shorter, but it will increase readout noise;
For camera manufacturers, the rolling shutter can achieve a higher frame rate, but when the exposure is improper or the object moves faster, partial exposure, skew, wobble and other phenomena will occur. This phenomenon of rolling shutter shooting is defined as the jelly effect.
The application with short exposure time (such as <500μs) is suitable for global shutter. When the exposure time is long (such as greater than 500μs), choosing rolling shutter can have lower noise and frame rate.
Examples of defects in Rolling Shutter
Take a look at the picture below. Imagine that each orange box is one pixel, and our image has only three pixels. When our hero climbs the stairs, the pixels are read one at a time, causing a lag in the last frame.