A secondary action is an action that results directly from another action. Secondary actions are important in heightening interest and adding a realistic complexity to the animation. A secondary actions is always kept subordinate to the primary action if it conflicts, becomes more interesting, or dominates in any way, it is either the wrong choice or is staged improperly.
The facial expression of a character will sometimes be a secondary action. When the main idea of an action is being told in the movement of the body, the facial expression become subordinate to the main idea. If this expression is going to animate or change, the danger is not that the expression will dominate the scene, but that it will never be seen. The change must come before, or after, the move. A change in the middle of a major move will go unnoticed, and value intended will be lost. It must also be staged to be obvious, though secondary.
A secondary action is an action that results directly from another action. Secondary actions are important in heightening interest and adding a realistic complexity to the animation.
If a secondary action conflicts with, becomes more interesting, or dominates in any way, it is either the wrong choice or is staged improperly.
Facial Animation Dangers
Generally, in facial animation, the movement is a secondary action, subordinate to the body's movement. The danger with facial animation isn't that it will dominate the scene, but that it will not be seen. The change in expression should happen before or after a move, changes in the middle of a major move will mostly likely go unnoticed.
Example: A sad person wiping a tear from their face
Primary action: The expression of the face is the primary action. This is because it is what will portray the characters sadness the best.
Secondary action: The wiping of the tear is the secondary action because a hand wiping a tear without the expression would not portray the emotion that is needed for the scene.
The hand wiping the tear would need to be carefully planned to support the facial expression. A big overwhelming gesture with a huge hand covering half the face wouldn't be acceptable. If the hand wiping the tear is to subdue it could be completely inconsequential. In which case there is no point in even having it there. If you make the hand fly past the face to quickly people will wonder what just happened and or whether they missed something. In which case it takes attention away from the primary action (the face), and you will have destroyed the feel of your scene.
In some scenes the expression will become the secondary action. Such as in a long shot where the character sadly turns to walk away. You need to make sure that the expression is seen but the primary action is the character turning to walk away. In this case you would need to show the expression either before or after the primary movement and you have to make it obvious, even though it is the secondary action. If you do it during the movement it will most likely never be seen. A change of expression in the middle of a major movement will go unnoticed and any intended value will be lost.
Making sure your secondary actions are subordinate:
A good way to make sure that your secondary action stays subordinate and your scene flows well the way you want it to be to.
Go through and animate the primary action, make sure that it looks the way you want it.
Then go through the scene a second time and animate the secondary action, making sure that it all works the way you want it to. And that it doesn't overwhelm or detract from the primary action in any way.
Then go through a third time to make sure that the rest of the animation relates to the primary and secondary actions the way they should.
Its simple and obvious I know. But I have made the mistake of trying to animate all the actions at the same time. And it's hard to keep track of everything that is going on. And it's harder to tell which actions are going to be the most dominant if you are animating them both at the same time. If you do it this way you will save yourself a lot of time and trouble because you will be able to compare your secondary actions to your primary ones the entire time and you can catch your mistakes sooner. Also one last thing to know about secondary actions is that you don't only have to have one. Some times you will have several secondary actions. In which case you should decide which ones are least important and make them subordinate to the others.
Secondary action adds to and enriches the main action and adds more dimension to the character animation, supplementing and/or re-enforcing the main action.
Example: A character is angrily walking toward another character. The walk is forceful, aggressive, and forward leaning. The leg action is just short of a stomping walk. The secondary action is a few strong gestures of the arms working with the walk. Also, the possibility of dialogue being delivered at the same time with tilts and turns of the head to accentuate the walk and dialogue, but not so much as to distract from the walk action. All of these actions should work together in support of one another. Think of the walk as the primary action and arm swings, head bounce and all other actions of the body as secondary or supporting action.