Avoiding the “digital motion” look

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  • #173358

      The “digital motion” look I’m referring to is a strange kind of smoothness and sharpness. I’m not sure how else to describe it, except to say it is extremely noticeable in HFR films such as the Hobbit and Avatar 2, and it is made worse by whatever horrible motion smoothing algorithms they are inflicting upon televisions.

      But, it’s completely possible to have this look occur at 24 fps, using high end digital cameras, including RED’s and Arri’s. Possibly it can even occur in film cameras, though every time I notice it it seems to be a digital camera. Some kinds of motion can cause it, and certain lighting setups can make it worse.

      My questions are:

      * Is there a common name for this issue?

      * Is this something that can be intentionally mitigated? Are there any rules of thumb as to how to avoid it?

      Apologies if I’m being a bit vague.




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    • #173374

        Check the term “Motion Cadence”.

        I don’t know it it’s what you mean.

        All I can say is some people is more prone to see the intra movement of frames than others.
        We did a little experiment among some friends checking different frame rates. Being shoot with 3 different cameras. From 24 to 240 on a high refresh monitor.
        We also check 24fps with different shutter angles. We try to use different screens and projectors and different viewing programs.

        It’s really a can of worms as there are lots of variables. Camera, camera motion, the motion inside the frame, monitor or TV, all the settings you can choose in each of them. It’s endless. And in top of that some people can see more differences than others.

        You can really get lost on it or simply use what you feel is the best and focus on more important issues.

        But remember that the camera and the viewing monitor/tv/projector are as much as important when checking. And no matter what you do people will experience it different than you because their viewing device is not the same as yours.


          One difference between digital and film cameras is rolling vs global shutter. Although cinema cameras like Arri and Red have very fast readout speeds (<10 ms) your brain might still pick out something there if you can even see it at 24fps (I definitely can’t see anything odd in, let’s say, any Deakins/Alexa movie when watched on a ‘controlled’ screen).


            Thanks for the answers, “motion cadence” sounds like the right term. I don’t think this issue is related to rolling shutter, which creates more of a skewed or warped image. And I even see this issue in CG, so it’s not really related to any particular camera technology.

            And I completely agree that it is a can of worms.

            For example, smooth camera motions which are too quick, but not quick enough. There is a bad middle ground where a camera pans quickly, but not quick enough to induce motion blur like a whip pan.

            Strong specular highlights, and having too much of the frame sharply in focus also seem to cause it.

            I’d link to examples, but I don’t really want to bag on anyone’s work. I have seen it come out of an Arri, so nothing is sacred. Never seen it in Mr. Deakins work though. 😉

            I think much of this may fall under general “rules” of good cinematography, so there’s no need to explicitly worry about this particular issue, just worry about getting the shot you want. But I was curious if it was something that others actively thought about when planning their lighting, composition, lens choice, etc.


              To through a spanner in the works.

              The term ‘motion cadence’ is thrown around too much.

              Your digital sensor will inherently perform differently to film. You’re dealing with the analogue movement of negative through a gate. Not a bunch of photodiodes being line reset. You’re probably seeing a multitude of aberrations in film like gate weave and so forth.

              However, it’s very important to note. The likelihood of there being a difference in ‘motion cadence’ between digital cameras is minuet.

              A CMOS sensor is inherently a line of MOSFET diodes; electrons absorb the magna of energy from photons, which allows the charge to bridge the gap between a PN junction – thus giving voltage proportional to the amount of light that hits x photodiode.

              A photodiode is shorted every y interval, and this is your shutter speed. If it’s an APS ‘global shutter’ (adding local capacitors), it still has a line reset (the line going across the horizontal row of diodes/pixels that resets them). It just adjusts the interval in which each line is reset, as the local photosite can hold the voltage (local capacitors).

              However – motion; the idea of each pixel receiving light over a period of time. Is the same. Adjusting your shutter (reset interval) will change this.

              Gabriel Devereux - Engineer

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