ROLLING SHUTTER EFFECT
| recording frame rate | = | s⁻¹ | |
| spinning frequency | = | s⁻¹ | |
| rolling shutter delay | = | ms |
| recording frame rate | = | s⁻¹ | |
| spinning frequency | = | s⁻¹ | |
| rolling shutter delay | = | ms | |
About the simulation:
The recording frame rate of the camera is set with the first slider, the spinning frequency of the object is set with the second slider, and the delay between the captures of the first and last row is set with the third slider. Precise values can be entered by clicking on the numbers next to the sliders.
The spinning object can be changed to something different through the drop-down list. You can also spin your own custom images by selecting the last option on the list.
It's possible to switch between a rolling shutter and a global shutter.
The simulation can be paused and continued at any time by pressing the pause button.
In reality, cameras capture multiple rows of pixels at the same time, but in this simulation, the images are captured one row of pixels at a time. In addition, while real sensors take some time to capture the light, the capture in this simulation is instant.
What is this a simulation of?
This is an interactive simulation of certain image distortions and optical illusions that can occur when filming a fast-moving or fast-spinning object. To better understand what this is about, watch the following video of a small, fast-spinning wind turbine.
In the video, two effects are at play: the wagon-wheel effect, and the rolling shutter effect.
The Wagon-Wheel Effect
The wagon-wheel effect is an illusion, which makes a recorded spinning object (like a wagon wheel in an old Western movie) appear to spin at speeds different from reality, even backwards. It's most noticeable when the frequency of the spinning object () is close to a multiple of the recording frame rate ()
In other words, if the rotating object is in the same position every time the camera records a frame, it will appear stationary on video. This explains the videos of helicopters flying with stationary rotors.
However, if the rotating object is in a similar position every time a frame is recorded, it will appear to be spinning slowly. If it doesn't quite complete a full turn every frame, it will appear to be spinning in the opposite direction.
The Rolling Shutter Effect
The rolling shutter effect occurs when a camera sensor captures an image sequentially rather than all at once. Digital cameras on the cheaper side, like those in smartphones, capture the image line by line, from top to bottom or side to side. This sequential exposure means different parts of the scene are captured at slightly different times.
This is important if the scene changes substantially while capturing a row. A rolling shutter makes a fast-spinning propeller look bent or wavy. The faster it spins, the more distorted it will appear. A fast panning motion might cause vertical objects, like poles, to slant.
Some cameras have (more expensive) sensors with global shutters, which capture the whole image at once and don't have the above-stated shortcomings.
