Animators by day Animation teachers by night.

Saturday, July 07, 2007

IK Is Not Always OK.


One thing I've noticed a lot of students do recently is animate with IK on for no apparent reason. For example, a character just walking forward in space and gesturing with his/her arms would be animated with the arms in IK. I'm not sure if this is a rookie mistake, laziness, or if people do it so they don't have to deal with orientation switches but, in my opinion it is very noticeable and it almost always looks wrong. If we just look at the terminology we're using we can get some obvious hints that will help you with your work method. "Inverse" means the reverse of something. So the opposite of FK, or forward motion, must be obstructed motion or motion impacted by an external element.

That external element makes perfect sense when it's something like a ground plane, table top, or any surface that your character may need to interact with. However, if a character is just walking around or standing still and gesturing and the arms are free of any external element, then IK stands out like a sore thumb and your animation looks like a puppet with arm rods. Movement begins to look externally motivated. You don't want to do anything that's going to break your "illusion of life". I love the Muppets as much as the next guy and those characters seem real to many people but Kermit's arms still look like their on sticks..... which is just bad IK.

-Adam

25 Comments:

Blogger Fränk Spalteholz said...

hi adam!

you are right! especially in the case of a walkcycle it makes no sense to use ik, course the energy comes from the shoulders so the arm should have overlaps. but that ik/fk-thing is annoying me anyway course an animator should not think like "aah that's a fk situation" or "uh how the hell to blend from ik to fk." the rigs in xsi are great in that issue, course they have a mixed fk/ik-setup. you can select the wrist and place your arm whereever you want like ik and you can also rotate the elbow and the shoulder at the same time without blending! thats great! wish to have something similar in maya. but maybe someone knows more.

1:47 PM

 
Blogger Benjamin De Schrijver said...

I'm a 2D animation student, but I gather it's just different for different people. Some just prefer to work in IK. It only looks like a puppet if you do it wrong... Whether you're working in IK or FK, you simply need to be in control.

3:00 PM

 
Blogger DJ said...

I have seen some poor FK stuff too.. limbs looking like stuck and not being able to move correctly for some movements. Especially if "breaking of joints" isnt done well.

So, I guess its more of the animator's ability or inablity with their animation that makes either IK or FK work.

personally, I am an IK guy. I ALWAYS animate in IK. Rare occassions I dont animate in IK are like walk cycles, but if theres any gesture, I would use IK. The reason is that I dont like counter rotations. and that if I change the rotation of the lower spine slightly, the whole silhouette is off and i have to rotate the arms out again and that makes me really frustrated.

May be I dont have a good FK workflow, but im looking forward for a thorough tutorial on how people work with their counter rotations.

I simply pick the hands and put them where I want, then use other controls to make it"look" like elbows are leading wrists (where ever applicable) and animate the shoulder controls to make it look like the energy is coming from them. And then, if I find that the spine rotation is off, I just fix it and i dont have to worry about hands again. I will manually add settles and overlaps by moving my IK control and making the wrist drag with rotations.

Thats what I am most comfortable with. It feels good when something stays where I put it. Often I am frustrated if anything rotates or moves when I moved something else, and I loose my "flow".

May be its just different people with different ways of working. but since a Doctor just said "Ik is not always OK", I will seriously look into rebuilding my workflow to incorporate the best of both worlds. But as Frank said, if such rigs are available, may it makes it easier!

DJ

5:20 PM

 
Anonymous Anonymous said...

"but I gather it's just different for different people."

eh.

ideally, the animator would not need to think about IK vs FK, but unfortunately, many do, and don't. using IK to move an appendage like its not planted on a surface like the table, or holding a hand railing, is just askinf or unnecessary work, and often looks poor.

so yes, they animator's goal is to be in control, but using IK when yo don't need it, is like driving a race car on an ice rink, instead of asphalt, voluntarily.

in my opnion at least.

5:20 PM

 
Blogger Matt said...

DJ - have you tried animating in FK but with a control that aligns the root to world space? So if you rotate the back the arm will stay at the same angle and it doesn't throw everything out. This is what helped me make the transition to FK, but of course being careful to make sure it doesn't feel disconnected from the body. I find polishing in FK ten times easier than IK as there's a whole lot more control over overlap, follow-through, arcs, all that good stuff.

5:40 PM

 
Anonymous Anonymous said...

in response to Matt's comment...is it always better to use world space for the FK arms? why?

6:26 PM

 
Blogger adxzun said...

hi doctor adam...great advice on ik and fk. however...could give tips on switching fk to ik when a hand or any other part of the body comes in contact with an object that would have to move along with it. thank you.

12:17 AM

 
Blogger TikiAnimator73 said...

I agree. I wish rigs would actually animate IK&FK arms on the same frame. It would be nice to move a hand out in space and then on the same frame, use the FK to rotate the hand at the shoulder pivot.

I'm a rookie that has used IK in the past to swing a baseball bat. During the anticipation, the swing looked like muppet hands. I should have had the driving force be the left (outer) arm which would have been in FK. The right arm would be the child with IK.

2:27 AM

 
Blogger Matt said...

anonymous - the reason I like it is that it allows you to change the pose of the back and shoulders without losing the arm pose, so you can deal with different body parts as seperate units and avoid all the counter-animation you would otherwise have to do with FK arms.

Its not the be all and end all though - if your character turns around frequently for example, it can confuse things. And its easier to lose the sense of connection between the arm and the body.

Comes down to personal choice at the end of the day, its just a solution I thought dj might find useful :)

4:41 AM

 
Blogger chintan said...

hey doc...

gr8 tips !.. i have one query.. so far i used to use the hogan rig for all the body mechanics assignments which we used to get.. but now i tried my hand on the new rig called "Andy".. its a human proportion rig... but the problem i m facing is how to get the hand in the right position using FK... because if i rotate it too much.. the forearm & the shoulders start twisting... i wonder how do u guys tackle that problem ??

thanks & regards,
Chintan :)

5:32 AM

 
Blogger Fränk Spalteholz said...

hey matt! that's a great tip! thank you!

10:30 AM

 
Blogger David Gray said...

Forgive my ignorance, but what is 'IK'? I've never heard of that before. Is it a CG term?

1:41 PM

 
Anonymous Anonymous said...

Thank u, Adam Burke, this post, like the the few before it, is SO helpful! I love what u guys are doing, and thanks for sharing, and being so unselfish with all this inVALUABLE knowledge=)

10:11 AM

 
Blogger dub524 said...

As for the Andy rig. If you click on the arrows next to the ik handle. You will see a twist fix in the channels box. Set that to a value of 1 to turn it on. Then control it by using the handle that is sticking out of the shoulder. That should fix the problem by moving that around.

12:19 PM

 
Blogger Dr.Burke said...

Thanks for all of the great comments. I'm enjoying the discussion it's created. The bottom like is IK and FK are both very useful but have their specific purposes. An animator who would say "I only work pose-to-pose" or "I only work straight-ahead" is limiting him/herself to an unfortunate degree in some situations and making a tremendous amount of work for him/herself in others. Matt brought up a great point of using aligns to compensate for counter rotations.

As for adxzun's request for advice on dealing with switches, you're often limited to what the program you're using allows you to do. Perhaps there are mel scripts floating out there to help you with switches if you're using Maya, but I know very little about that sort of thing. My only experience has been with the proprietary program we use at work so I feel a bit limited in giving technical advice. What I can tell you though is that sometimes it's just plain hard and you find you have to get in there and muscle the work into shape for the transitions. As comprehensive as Pixar's program is, even we have to get in there sometimes and force things to do what the software isn't giving us or come up with a creative solution. Animation, when it's being done properly, is always going to be difficult. Technology will continue to improve, but it's NEVER going to be what makes your animation great.

Rick Sayre, a gifted technical supervisor at work once said, "Every time we pull on the technology lever to solve our problems...it breaks off in our hands." Keep talking to each other. It's how we all learn.

-Adam

8:58 PM

 
Blogger DJ said...

Matt: Thanks for the advice. I will surely work on FK to find a "workflow".. ill start with basic excersizes sometime soon...

My mentor Michelle meeker told me to try FK with my class 3 assignment in AM. I ended up not finishing it because I couldnt get my head wrapped around it.. so I ended up starting a new piece of dialogue and with IK I finished it in about 5 days. At the end of it, my class 4 mentor Dave Burgess said that he couldnt see that I used IK and that I hid it pretty well and he thougth I used FK until I told him.

So, thats my situation now. But i understand having a wide range of tools at hand. I shall work on it, but i think, if you are used to it, you can make ik work well.. For me, it is very much faster than working in FK most of the times.. Its just because im more used to it I guess..

DJ

9:54 PM

 
Blogger Amrit Derhgawen said...

I agree with Doc.

I never like to use IK unless I really have to (e.g in push/pull etc). IK feels kinda like I'm writing with my left hand. For me its definitely less intuitive. Normally, I just don't feel comfortable with IKs. One advantage of FK arms over IK is that you get most of your arcs for free.

I really don't care much about counter-animating and stuff. When you animate you make bunch of pretty looking drawings in such a way or sequence that it create an illusion of life. So, all I care about is creating that illusion. It doesn't matter how I create it. I just create it, somehow.

So, I don't think that there should be anything like IK vs FK. They are all good and helps an animator do his job efficiently. So, whatever you use.... just make sure you've got 100% control over it and you're not breaking the illusion of life at any cost. I think its just a matter of preference. Use whatever makes you fee comfortable. For me FK works great. :)

-A

12:03 AM

 
Blogger chintan said...

Hey dub524,

Thanks a lot for the help buddy... it really solves my problem... thanks to all of the guys who comment on the posts ... i do get to learn from all your opinions... just like the dr. Burke said "Keep talking to each other. It's how we all learn."

thanks a lot
Chintan :D

1:18 AM

 
Anonymous Paul said...

I had a student last week working with a character that flies, and he wanted to know how he could get the hands and feet to follow the character around easily when he moved him. I told him to use FK! He'd been left with the impression from a previous class that all characters had to have IK rigs.

11:39 AM

 
Blogger Jean-Denis Haas said...

I'm so used to IK rigs at work, it's hard to go back to FK. The arms work in a FK/IK manner though, so we don't get that muppet feeling. IK is great for shoulders, ankles, chest, etc. because it allows you to do fixes without destroying your arm/head, etc. poses. Plus it lets you pose your character very quickly.

If you don't have a rig that supports IK/FK arms, I would stick with FK though, because unless you key every frame or you pay really close attention to your animation, the arms will have that disconnected feeling to them.

2:06 PM

 
Blogger Cameron Fielding said...

Maybe this thread is getting tired now, but I just wanted to add something about the IK FK thing...

I guess it depends on what you're animating, and the style of the animation.

For example, animation with a traditional look ( i.e "cartoony" ) really does seem to work better with an FK approach, because the actions and gestures are "summaries", boiled down to the core of a whole buch of complex movements - for this you may find that FK will help you work for directly in this mindset.

With realistic human animation, or creature animation - I like to use IK for the arms. The reason is because humans really do use their hands a lot - in everything - even if their hands are just dangling or idling they still project subtle gestures, and are constantly balancing the body. Because of the complexity of the mechanics of a human arm - a person CAN move their hand and make it appear to LEAD the movement of the upper arm and forearm, despite the fact that this isn't the case. This is the part of the beauty of the way real creatures and humans move. Because IK directly lets you interact and pose in this fashion, I like to use it to HELP with this kind of motion.

But, as always - were all going to do what works best for us.

11:20 AM

 
Anonymous Anonymous said...

Hi this is rahul, tell me pls which is good in fk and Ik because i am fk user basially, but someone tell me ik is more helpful than fk.
Now i am working in ik but i am finding too many problems ik during animation, i am not able to give proper action. Some time it look hand is stuck somewhere during animation because i am not able to match with shoulder movement it looks jerky. so pls give me guidance which is more helpful in animation for future purpose. http://www.youtube.com/watch?v=OYazUlcep8Q
just check my work which is totally based on fk.

10:05 AM

 
Blogger Rahul said...

give me reply pls.

10:17 AM

 
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