The rolling shutter effect happens when the scan lines in a video imaging sensor are captured at different times rather than all at once. Many cameras with CMOS sensors show the effect, while most of the ones with CCD sensors do not. For a more visual explanation, watch this YouTube video:

Remember that rolling shutter can cause a moving object to appear in the image at a different location from where you would expect it. Since the scan time is a fraction of the frame time, the displacement due to rolling shutter will not be larger than the distance the object would move during one frame time. If the object can only move a "small" distance in each frame then the rolling shutter distortion will also be small.

Tip 1. If the object moves along a straight line, orient the path of motion along the x-axis of the frame so the rolling shutter distortion is minimal. For example, to follow a falling object, tilt the camera by 90 degrees. To follow the motion of a cart on a ramp tilted by 30 degrees, tilt the camera by 30 degrees. As always, the optical axis of the camera should be perpendicular to the path of motion to minimize parallax distortion.

Tip 2. Since the scan time is a fraction of the frame time, you might be able to reduce the effect by increasing the number of frames. That is, try to make the total distance the object moves large in comparison to the rolling shutter displacements. There are two ways to do this:
  • Make the motion last longer, such as by moving the camera farther away from a falling object. Of course, it may not work if the motion is repetitive, such a circular motion. In the YouTube video above, we intentionally limited the projectile motion trajectories to a height of less than 10 cm to make the rolling shutter effect very obvious. For a trajectory height of one or two meters the rolling shutter error would be just a few percent (depending on what camera you use).
  • Decrease the distance the object moves in each frame by using a camera with a high frame rate. Most video cameras today run at 25 to 60 frames per second (fps), with 29.97 fps being the standard in the US. Some cameras have options of 120 fps, 240 fps, or even higher. See the page on high speed cameras.

Tip 3. Treat rolling shutter as a systematic error and apply a mathematical correction for it in your analysis.

Tip 4. Use software that is supposed to eliminate the rolling shutter effect from the video. Be careful, though, because such software is designed to make videos of ordinary scenes look less unpleasant, not to make them more accurate for motion analysis.