Global exposure and rolling shutter exposure are common camera exposure methods. Generally speaking, CCD cameras have global exposure, while CMOS cameras have rolling shutter exposure. So, which of these two methods is better? In other words, what is the difference between the two? So, let's start with the definition of the two.

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Global exposure

The global exposure method is relatively simple. In other words, after the aperture is opened, the entire image chip is exposed at the same time. Therefore, the exposure time is related to the switching speed of the machine. Since it is related to mechanical motion, there is a theoretical minimum exposure time.

Rolling exposure

As the name suggests, the way of rolling shutter exposure may be related to the concept of rolling shutters. In this type of exposure, when the aperture is opened, there is still a rolling shutter with a certain interval to control the exposure time of the sensor. Note that, as shown in the figure below, the way of rolling the blind is from left to right. Therefore, the length of the exposure time completely depends on the opening size of the roller blind and the speed of the roller blind. In other words, the faster the rolling shutter moves and the smaller the distance between the rolling shutters, the shorter the exposure time of the sensor. Therefore, the rolling shutter exposure method can have a shorter exposure time.

The movement of the roller blind is shown in the figure below: when the roller blind is moving, the sensor at the opening of the roller blind can receive light.

Pros and cons of both

(1) The advantage of global exposure is that all pixels are exposed at the same time. The disadvantage is that the exposure time is limited, and there is a minimum exposure time that is mechanically limited.

(2) The advantage of rolling shutter exposure is that it has a shorter exposure time. The disadvantage is that because the line-by-line exposure is taken at different times, if the image is moving, there will be obvious smear. Therefore, rolling shutter exposure is not suitable for shooting moving objects.