12 Rules of Animation as described in Illusion of Life by Frank Thomas and Ollie Johnston

Rule 1: Squash and Stretch, the purpose of which is to give a sense of weight and flexibility to an object. This can be for simple objects or for complicated objects, for example a bouncing ball to a fully drawn character. If exagerrated this can create a ratehr comic effect but in realism it is preffered that the objects volume looks liek it hasnt changed shape at all.

Rule 2: Anticipation is used to prepare the audience for an action to build up to a climax or anti-climax in a scene. This can be things like the pull back in a baseball players swing or a bend in a balet dancers knee. This technique can also be useful for not so physical animation, for example someone looking off camera for another character to enter the scene.

Rule 3: Staging, this has the same meaning as it does in Theatre and in Film. It's purpose is to direct the viewer or audience to what matters in a scene, to what's relevent, what's happening or indeed what is about to happen. To quote Ollie Johnston and Frank Johnston it's " the presentation of an idea so that it is completely and unmistakeably clear", wether this idea is an action or a personality.

Rule 4: Straight ahead action and, pose to pose. These are the names given to the types of approaches used in the drawing process. Straight ahead action means to draw or animate frame by frame from start to finish. Pose to pose involves starting with drawing a few key frames such as the start, middle and end pose and filling in the intervals. Straight ahead creates a more fluid illusion of movement and is used to create a more realistic action sequence although it can be hard to create exact, and convincing poses.

Staight ahead

Good points:

• very open for creativity during the keyframing work;
• can result in more fluid and natural looking animation;
• done for all frames in a sequence it totally eliminates the use of computer interpolation;
• a talented artist in a good day can achieve very spontaneous and elaborate results;
• specially good for fast, wild actions;
• only after finishing the animator will know how the scene ended up.

Bad points:

• it's easy to come to dead ends, where work may have to be discarded and redone;
• hard to make the character respect "marks": be somewhere or grab something at a definite frame;
• hard to create strong poses, well staged, solid and appealing;
• the resulting set of keyframes will probably be complex and disorganized, hard to work with;
• only after finishing the animator will know how the scene ended up.

Some might also add: more work while animating.

Pose to pose works better for dramatic or emotional scenes, where composition and relation to the surroundings are essential. In CGI it is more pose to pose based where things like IK and hierarchy's designed to create deformations remove the need for the animator to over see every frame however it is necessary for the animator to overlook what has been created and make sure the other rules are applied

Pose to pose

Good points:

• more control over the results, easy to respect marks;
• less room for pitfalls;
• more work in less time;
• the created extremes (plus soundtrack) can be used as animatic for critique and corrections;
• with planning, there's a better chance to come up with elaborate poses and moves;
• done every N frames or so, results in a clean layout of keyframes, easy to work with;
• randomness is played down.

Bad points:

• easy to result in “robotic”, dull animation;
• less room for creativity while creating and keyframing poses;
• randomness is played down.

Some might also add: requires proper planning, sketches, etc.

Rule 5: Follow through, and Overlapping action. These techniques help to put across realism in movement and show how the animation follows the laws of physics. Follow through means that if a character suddenly stops then his arms may still move or hair wills till flow. Overlapping action is the tendency for the parts of the body to move at different times. i.e an arm will move out of time with the head and so on. There is also a technique called "drag" where a character moves and the rest of him has to catch up. This can be used in inanimate objects like clothing and antenna on a car. The torso of a character (Human) is the core, the arms, the legs etc follow the toro's movement. Like with Squash and Stretch you can create a comic effect whereas the realistic  animation must be exact to produce a convincing result.

Frank Thomas and Ollie Johnston also developed the principle of a "Moving Hold". This is when a character not in movement is rendered completely still to draw attention to the main action, although this is considered dull and should be avoided.

Rule 6: Slow in, Slow out. All animated objects must accelerate and decelerate, this helps to create realism. This goes for characters that are doing 2 extremes such as sitting down and standing up. Inanimate objects also apply to this rule like a bouncing ball.

Rule 7: Arcs. Most human and animal actions occur in an arched trajectory, an animation should reproduce that for realism. This  can apply to a limb moving by rotating a joint or a thrown object moving along a curved trajjectory. The exception is mechanical movement which is rather linear.

Rule 8: Secondary Action is when you add another action to help the main action. In walk cycles this can be evident when the characters arms move with his legs The job of a secondary action is to draw attention to the main action not to draw it away.

Rule 9: Timing refers to how many frames there is for a given action, which translates to the speed of the action on film. When done correctly this gives the animation more realism and makes them appear to abide by the laws of physics.

Rule 10: Exaggeration is great in use of a comdey effect and is incredibly useful in animation as it can alleviate a dull scene. The classic defination used by Disney was to remain true to reality but, to present it in a wilder, more extreeme form. Other forms of exaggeration can involve surreal or supernatural elements. It is important not to over do this and if your secene has a lot of elements you should balance these accordingly so youdon't over power the viewer.

Rule 11: Solid Drawing. This means that the animator should be able to take into account, 3D space, Volume, Weight, Balance, Light and Shadows. This requires that the animator takes art classes and drawing from reality. Ollie Johnston and frank thomas warned about twining as well where a character is posed the same on both sides.

Rule 12: Appeal is to a charcter what charisma is to an actor. Appeal doesnt mean sympathetic, villains and monsters have appeal also. it means that your character is interesting.


A link to Frank Thomas and Ollie Johnstons Website:
http://frankandollie.com/PhysicalAnimation.html