I'm putting together a very basic software to animate a few pixels frame-by-frame. I've skimmed through Richard William's Animator's Survival Kit in the past and noticed most traditional animation uses 24fps and he used to "animate on twos" for most motion and on "ones" for fast motion.

Since my tool will deal with frame by frame animation I'd like to make use of those principles, but I am constraint to 30 fps. Because of this, I'm wondering how would I workout at what frame interval(every frame, every two frames, every three frames, etc.) a 'keyframe'/changed frame should be placed to look good ? Is there a way to work that out arithmetically ? Does it make a bit difference/ is it safe two stick to twos even for 30fps ?

1 Answer 1


Yes, repeating every other frame works the same way at 30fps as it does at 24fps.

Animating on twos is done not because it looks better, but because it means less drawing and you can 'get away' with it. Nothing stops you from drawing every frame if you want the smoothest possible motion, and nothing prevents you from repeating a frame indefinitely when there is no motion.

If you really want to work at 24fps, you could always animate 'as though' you were working at 24fps -- your work will look sped up when viewed at 30fps -- and applying a cine expansion (3:2 pulldown) as a final step.

  • Pretty thorough answer Jim, thanks! I thought about 'getting away' with less frames...24/2 = 12 (the minimum amount of frames needed for the eye to perceive continuous motion) - is that plausible ? Jan 30, 2013 at 13:37
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    @GeorgeProfenza The 12 fps comes from that the silver movies was/are played back at 24 fps. Disney found that 12 fps still worked but reduced the work to 50% (and instead photographing two frames for each drawing instead of one). The "12" is just an accident/consequence from the fps used for movies (although, 8 or 1/3 obviously didn't work so well). There is nothing wrong trying to use 10 fps if you're using 30 fps.
    – user2995
    Jan 31, 2013 at 3:07
  • Thanks for the explanations Ken, pretty interesting stuff ! :) Jan 31, 2013 at 12:16

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