Rolling Shutter effect from a typical CMOS digital sensor. Photographed by author.

Rolling Shutter: Problems and Solutions for Law Enforcement Cameras (Part 1)

Multi-part series on Police body cameras from the perspective of a cinematographer and forensic consultant.

Not all images were created equal.

Body Worn Cameras (BWCs) are in a grim technological state when compared with Action Cameras (ACs) like the GoPro. BWCs marketed to law enforcement cost more and are substandard in image quality to the options available on the AC market.

Combine: shaky input, low bit-rates and wide angle views and you have the perfect storm for low quality video.

TO SCALE: Selection of body worn cameras and action cameras. Diagram by Author.

In reviewing footage; will you be able to read the text on their shirt? Is that a tattoo or a birth mark? Why does that thing look warped?

ROLLING SHUTTER DISTORTIONS: A stable image compared with three distortions symptomatic of a fast moving camera with a rolling shutter. Images by Author

Rolling Shutter Effect

MID-BLINK: Probably scanned from right to left. Taken on an iPhone. Image used with permission.

THE PROBLEM

Rolling shutter is the root cause of: jello cam, wobble cam, skew, fluorescent light banding, partial exposure and many other image quirks.

This problem is fairly new. It arose in the transition from CCD to CMOS sensors. Both sensors were invented over 50 years ago; but by 2007, the video market largely transitioned to CMOS which offers more resolution, better light sensitivity and battery life.

ROLLING SHUTTER: Examples pulled from the web. LEFT: Propellor Blades RIGHT: Throwing a frisbee.

TEMPORARY SOLUTION

There are several software solutions that will un-skew diagonals which result from a panning camera but these solutions don’t work with complex curvature, fluorescent light banding and higher frequency distortions found in jello/wobble cam.

HARDWARE SOLUTION

The rolling shutter effect of CMOS chips need to be fixed during image capture. This must be done with better chip processing.

Few people know the problem exists and manufacturers are not inclined to address it. Cinematographers have been demanding hardware fixes since 2007 and some manufacturers are now claiming Global Shutter — the gold-standard of image capture.

How long until supply meets demand? What else needs fixing?

ABOUT THE AUTHOR

DANIEL VOSHART combines his background of cinematography and architecture to provide forensic video consultation and 3D reconstruction. He received a BA from Ryerson University and an M.Arch from the University of Toronto.

• PART 2: Low Bitrate (March 2016)

UPCOMING

• PART 3: Auto Exposure (April 2016)

FURTHER READING ON ROLLING SHUTTER

• Before Digital: Origins of the Rolling Shutter (Lindolfi 2007)
• Global and Rolling Shutters (Red 2014)
• Distortions by Michael Stevens (V-Sauce 2014)
• Rolling shutter tests (Cinema5D 2015)