If you’ve ever snapped a photo of a plane’s spinning propeller, and then scratched your head over the bizarre results, this hypnotic Gif will help you understand what exactly went wrong — although nothing actually did.
Digital cameras using a CMOS sensor often employ something called a rolling shutter. It’s not a physical shutter that rolls across the sensor, though; it’s actually referring to how image data is read off the sensor line by line, instead of the data from every last pixel all being read at the exact same time, which is often referred to as a global shutter.
The process of reading the sensor’s data line by line happens very fast, nearly instantaneously. But if an object in frame is moving even faster than that scanning process happens (like, say, a spinning propeller) it can result in bizarre visual artifacts.
An imgur user who goes by the handle Hunter5625 wanted to better understand this phenomenon, so he used the Desmos online graphing calculator to plot out an animation featuring a rolling shutter versus a spinning propeller. A blue trail is left where the propeller intersects with the rolling shutter’s scanning process, revealing the same sliced up pattern that so many spinning propeller photos do.
So what are you supposed to do if you want to snap a photo of a plane’s propeller and have it actually end up looking like a propeller? That’s easy — just go find yourself a digital camera with a global shutter. They’re most often employed in digital video cameras with CCD sensors, so the tradeoff might be a hit in image resolution.
Photo by Soren Ragsdale