I think, it's open when you want to push the emotion a little further, or to exaggerate it. I was thinking... if I laugh, i just laugh with jaw closed, but if I laugh really loud, my mouth is open.... if somebody crys it's possible with mouth closed, but cry loud. with mouth open... when you're mad, it's closed, when you open it you show your teeth.. I think you would open the jaw much more with a silent shortfilm then when the character is able to talk... I'm not sure if I'm right, but thats what i think cheers!
Hmmm. I've never really thought about this before, but maybe mouth position could be thought to be more related to the inward/outward projection of the emotion experienced by the character. Appeal definitely comes into it, but there are also acting/human behaviour cues that also influence things.
Closed smile, for example, suggests something internal in its weak form, and possibly smug in its strong form. Open smile is an abundance of happy times that cannot be contained - an outward projection of positive energy.
This thinking could probably be applied to other emotions, also.
Furthermore, open mouthed expressions carry with them a certain potential for subsequent action, so where a character goes next has an impact. It's easier to start talking from open, or breathe deeply for example; path of least resistance, and all that.
Whether or not a mouth should be open or closed when at rest is down to the character, both in terms of design and personality. I would judge it on a case-by-case basis.
Well, it all depends upon what works for your scene or what the motivation is for your character. Every choice we make should be based upon what the character is feeling and secondarily what is going to be more appealing to look at. So a lot of elements go into that and how you are thinking about your shot is going to determine your choices. But I'll throw out a few examples for you.
So lets say we have a character that is talking to someone that they don't really like but want to be nice to. A closed smile might be a good choice here. Because a closed smile is closed it makes it look less open and a bit more defensive. Another example would be for sadness. When a person is on the verge of crying and they don't want to. Yes you could have a person with an open mouth and get a very strong idea of sadness. But by having the mouth close and showing that the person is fighting to control their crying it becomes a much more powerful statement. You aren't just showing someone who is sad. You are showing someone who is sad but is also thinking about himself, his world, and how he impacts the people around him. Now a lot of detail goes into doing something like that, you cant just close the mouth and get all that great information, but it is an example where that choice could be made.
Another example is for purely animation based reasons. So lets say we have a character that is going from a happy expression to a surprised one. so we have the character going to a surprised open mouth pose. That cliche one you and everyone else has seen a million times. If we posed out the smile shape with an open mouth, when we went to the surprise it would work, people would understand it just fine. But if we posed it with a close smile shape when he opens his mouth the change is going to be way bigger. The graphic effect of the movement will be amplified while still retaining the core idea.
Other reasons that a character might smile with their mouth closed is purely character driven. If you had a person who was not happy with their teeth you could say that they trained themselves to smile with their mouths closed. But when they laugh their mouths open because they can't help it. It would be a fun bit of character. To show a shot with a person smiling with their mouth closed and then they start laughing and you see that they have braces or something.
Really the reasons you choose one style or another depends upon a lot of things. But ultimately its all about doing what works best for your shot and your character. My rule of thumb is that for every choice you make acting wise there needs to be a reason that you can explain behind it. either acting wise or animation wise. If you can't explain it, then you need to go rethink it. Hope that makes sense and helps.
I asked this question to Matt Finch during a skype discussion. He first responded:
There are plenty of people who smile with it open. You forget, animation is infinite, there is no answer. When you get to an acting shot, you have to look to yourself. There are mechanics physics, but there are choices and character. When you talk about choices like why a mouth should be open there is really no answer.
If you want appeal, all appeal is in a nutshell is simple shapes easily identified by any viewer. Appeal is a circle, a line, a box, a sack
Admittedly, I'm often vague trying to pin down the question I wish to ask. Thankfully, the DVD case for Megamind happened to be sitting on my desk. The below is a poster of the same film. Two characters with a similar expression, with a few important differences.
Metro man is a stereotype. The American man everyone wants to be; a touch of superman, a touch of Brad Pitt, a touch of Clark Gable. When a confident man smiles, he shows his teeth.
Metroman is a stereotype, his core of his character is a stereotype, he is what everyman wants to be, he is loved by others, he goes out on top.
Confident characters stay more symmetrical, however, a confident, arrogant, cocky smile may lean towards being assymetrical, with only one side of the mouth open, kind of like a smirk meets smile. This is usually a choice that will be made to show a character the audience needs to be uncertain of; their intentions are hidden.
However, remember. Animation is observation, you have to always be observing life.
This is where I feel my studies were focused. Yes, I love getting infront of a camera, observing nature etc. However, character can also be built upon stereotype. It helps people become familiar with a character.
Let's look at primitive expression:
Number one and four: The chimp cannot contain his excitement, its released through the mouth. Could you argue that a more dignified person can be shown through a closed mouth? Take a look at the Kate Middleton painting as an example. Going through history paintings, how many portraits show royals with open-mouthed smiles?
Number five shows a submissive expression. I was fascinated watching Bobo Smith's 11 SC entry for September 2011. You could argue that his lady standing under an umbrella, takes advantage of both the closed mouth regal (used at the start), before the more submissive open mouth shapes (used during speech).
Another submissive mouth is used in Liane - Cho's December 2011 animation. It is, however, pulled further back and shaped into a sneer. Great work!
Number two: The chimp is aggressive. Yes, this may open to release the rage, but currently it is contained within a pressure cooker.
Well, I've finished rambling for now. Probably need to tidy up this post sometime and include a conclusion. We will see.