01 Feb 2015

Stop using rolling shutter cameras for action movies!

  • Written by 
Terminator Genisys Rolling Shutter Terminator Genisys Rolling Shutter Paramount / RedShark

Index

RedShark News Technical Editor, Phil Rhodes, explores an unfortunate practice on action movie shoots and a sensible solution.

Can we please stop using rolling-shutter cameras for action movies?

We've talked about this before, but the existence of semi-visible muzzle flashes in the recently-hyped trailer for Terminator Genisys coincides with a few conversations I've had recently which imply that quite a few people still don't quite get what's going on here.

Most people are aware of the core phenomena behind rolling-shutter cameras – the exposure doesn't end at the same time for all of the pixels on the sensor. This leads to skewed verticals, for instance, during sharp pans or strange vertical compression effects during fast tilts. Software has been written which attempts to fix the problem and, in some circumstances, can work well, but some kinds of motion can defeat even the cleverest algorithms. Even more problematically, if there's a large, sudden change in brightness level during the period the sensor is reading out pixels, we get flash banding, as here:

rsn_rollingshutter_terminator_1.png

Here we see the lovely Emilia Clarke, she of "dragons" fame in Game of Thrones, firing the sturdy Desert Eagle, beloved of zombie- and robot-slaying motion picture protagonists everywhere. You've probably already noticed the reason for my facetious tone, in that we can, in fact, only partially see Emilia doing this, because the Alexa XT with which the scene was (according to IMDB) shot happened to be in the middle of reading out a frame when she pulled the trigger. Yes, the Alexa is a rolling-shutter camera, despite its otherwise stellar reputation, although it's not very rolling shutter. To be completely fair, on a film of that scale, they could have chosen to work with the mechanical-shutter version which could have mitigated the problem. But not to worry, we get the other half of the flash a moment later, when she fires another round. Sort of.

rsn_rollingshutter_terminator_2.png



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Phil Rhodes

Phil Rhodes is a Cinematographer, Technologist, Writer and above all Communicator. Never afraid to speak his mind, and always worth listening to, he's a frequent contributor to RedShark.

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