At frame rates of 24fps (the current US movie standard -- very close to the European 25fps TV standard), many 'fast' motions produce 'aliasing'/'strobing', including wagon wheels, airplane propellors, etc. Fast 'pans' of the camera will also produce unpleasant strobing/stuttering effects if a surface has a repetitive pattern. I once did an analysis to try to figure out what the 'maximum non-aliased pan rate' for a still image should be. I concluded that the pan couldn't move more than 1/2 a wavelength per frame for the highest spatial frequency (in the panning direction) in the image. That's an extremely slow pan for an image of any significant resolution. Of course, this slow a pan, or this fuzzy of an image is completely impractical, so you will always see artifacts. Hollywood people know how to minimize these artifacts, but amateurs violate these rules most of the time. Modern computer graphics cards can now render photorealistic 3D 1920x1080 at 60fps _in real time_, and some movies this past year are available in frame rates higher than 24fps. Many Hollywood people hate this non-film 'look', as it eliminates most of the last vestiges of the viewer not being in the scene along with the actors. Animated graphics can generate the correct frames for any frame rate you want, so they are 'frame-rate independent'. Movies can also be made 'frame-rate independent' by using sophisticated computer vision algorithms to figure out which objects are moving relative to other objects; once this is done, the 'in-between' positions can be simulated. In fact, the basic 'motion prediction' elements of the various MPEG standard video compression algorithms do a crude version of this analysis simply to reduce the number of bits that are required to be coded. At 04:20 PM 6/24/2013, meekerdb wrote:
On 6/24/2013 3:47 PM, Cordwell, William R wrote:
Speaking of wheels turning, in many old movies, the stagecoach wheels seem to be turning backwards--is that simply an effect of the film frequency and the wheel angular frequency?
Yeah, that's just frequency aliasing as the film frame rate and the wheel spoke rate cross over. You also see it in movies of aircraft propellors as the engines start up.
Brent Meeker