Vision Imaging Sensors: Global vs. Rolling

When developing a camera solution for an imaging need, there are many considerations to evaluate. Lighting, the size of image area, resolution (how many pixels do you need to see your object clearly enough for your objective), how fast you need to transfer your image, where are you going to store your image, etc…

Probably the easiest but one of the most important considerations is what do you need your vision sensor to do. Are you taking a picture of a static object (not at movement) or are you obtaining an image that is moving fast and you need to freeze or capture that image in milliseconds?

The simple difference in figuring out which of the two types you require is dependent on the basic technology of how the image is captured.

A global shutter exposes ALL of its pixels at the same time to the image, thus getting the whole image at once.

A rolling shutter exposes EACH LINE of pixels (while incredibly quickly) sequentially and at a different time, capturing one line of pixels at a time. Thus, the pixels exposed on the first line of the sensor might have a different image than the pixels exposed on the last line. This can cause the image to blur and look inconsistent.

These differences are usually reflected in the cost of the sensors. In general, rolling shutter sensors cost less than a global shutter sensor of the same resolution, as the slower acquisition technology requires less circuitry. Or conversely, a faster sensor is more expensive because it costs more to manufacture, in order to take all of the image at once.

Interestingly and for this very same reason (less circuitry), some rolling shutter sensors have lower internal noise levels and can usually collect light better thus having better sensitivity to low light and extended wavelengths.

In practical applications, the distinction is clear: rolling shutter image sensors are typically employed in security and consumer cameras, whereas the demands of industrial and aerial imaging usually necessitate the precision of a global shutter.