Earlier quoted context omitted.
Another interesting problem would be the generation of filler pictures (I don't know the correct term). Normally there is a person who draws keyframes at a much lower framerate. Other animators then fill in the frames between to increase the framerate.
That's the problem with animation using bitmaps (or physical artwork): the in-betweens have to be manually drawn. Hence much animation is outsourced to studios - typically in Korea, and occasionally Japan - consisting of armies of animators and artists. With vector graphics - where the lines and fills are mathematical objects - automatic 'tweening' becomes possible. Anime Studio ( http://my.smithmicro.com/anime-studi…
Sometimes a perfect interpolation, or even something based on a physical model doesn't feel right, isn't what is expected.