Is the name of the phenomenon of an image staying in the retina for a short period of time, when another image appears, this phenomenon gives the illusion of movement. In others words, image after image with this phenomenon creates motion.
Principles of animation:
The principles of animation were introduced by Ollie Johnston and Frank Thomas in 1930, they were animators at Walt Disney Studios.
These principles were and are still being used for animators in lots of films, tv shows, gaming, and any other way of animation. With these principles the animations look more realistic, for example the bouncing ball looks better and more realistic with the squash and stretch principle.
12 principles of animation:
1.Squash and stretch. This principle is commonly used by animators, it consist of giving a sense of weight and flexibility to an object, it could be used on simple and complex objects. Here is an example of squash and stretch used in "ratatouille" http://www.youtube.com/watch?v=jwLKPDJqldw
2.Anticipation. It is used to prepare the viewer that a character is about to perform a major movement, like kick a football, it is not just kicked, you have to put your leg backwards and then kick it. This movement its used in almost all the movements people do in real life.
3.Staging. An action should tell the viewer the attitude, mood, reaction or idea of the character and it has to relate to the story and its continuity. Also using different camera shots or angles of the same action in the timeline helps in telling the story and making the viewer interested.
4.Straight ahead action and pose to pose. Consist on animate key frames and then fill the gaps, it is also known as frame to frame animation.
5.Follow through. It is when the body of the character stops, and other parts continue to catch up to to the characters body, for example long hair. In this link you could see an example of this principle http://www.youtube.com/watch?v=Loo41xVIb_I
6.Slow out and slow in. There are more frames when an action starts and finishes than in between the starting and finishing point.
7.Arcs. Most actions follow a circular path to give the animation a realistic movement, as in real life, our arms and head move in an arc when walking, running, etc, the animals do the same, this is why this principle is used in animations.
8.Secondary motion. It is giving a character already moving another action, for example a character walking and smoking, the second action it would be smoking, adding more dimension to the animation.
http://www.youtube.com/watch?v=vKZMo1JZk74 in this video Figaro snuggles down into the blankets.
9.Spacing and timing. Basically this principle says: the more drawings between poses slower and smoothly the action will go, the fewer drawings make the action faster and crisper.
10.Exaggeration. Its just like the word says "exaggerates" any movement to make it funnier or more dynamic.
11.Solid drawing. This is the basic principles of drawing form, weight, volume solidity in the illusion of 3d.
12.Appeal. Its the principle that says the animation as to be likeable, with charisa, make the viewer laugh or cry, being cute and cuddly.
Resources:
http://en.wikipedia.org/wiki/12_basic_principles_of_animation
http://minyos.its.rmit.edu.au/~rpyjp/a_notes/anim_principles.html
http://maximized.co.uk/animation/
http://vimeo.com/49092833
http://www.animationtoolworks.com/library/article9.html
