IK vs FK


Most debates (or arguments) inside an animation studio have a correct (or at least) best case solution and eventually end. But there’s one type of debate that never ends, and it continues to come up project after project. Essentially, every time a different combination of people starts working together the battle between FK and IK will rear it’s ugly head… every time.

It doesn’t usually start out as an IK vs FK debate, but once you’ve peeled away the layers that are concealing it… and it continues to keep going, it becomes obvious that’s what you’re talking about. Every time it happens it makes me smile. Because once you realize that’s what you’re talking about, you won’t be able to end the argument by selling the virtues of your preferred method. You realize you’re all wasting time repeating the same argument and you have to change tactics to find a way to end it. This is where I tend to lean on my experience, and reach back into my archive of projects to highlight the pros and cons and their end result on the final product. Only then do people realize they’re in a holding pattern and there’s not much point continuing to debate it. Usually the loudest, most passionate voice, wins. Often this is a supervisor, or someone that has a say over the other team members’ jobs. That doesn’t mean that person is right though, because neither IK nor FK is the right solution 100% of the time.

I’ve come to the conclusion that it comes down to the way each person thinks about their workflow. Depending on how their brains prefer to work they’ll lean one way or the other. The problem is that there are a good number of people that will stamp their feet and say their way is the best and even more people that will blindly follow them based on their respect for that person in the industry. When this happens it spreads and you end up with talented people fighting for solutions they’ve not really thought through. Understandably they’ve been taught one way and they’ve gotten used to that method. That’s how it should work. The point of teaching is to bypass the mistakes of previous generations and allow new generations to solve new problems without wasting time re-inventing old ones. But this happens to be a debate with more than one solution, and if both are not taught with complete understanding of their virtues then the student will end up in this debate at some point. Most animators tend to fall into one camp or the other, and that’s where the issue lies.A partial solution is having IK built over FK, or FK built over IK. But ultimately, depending on what order you chose, one of them isn’t really pure and can’t be switched to without messing up the workflow. Values in the graph editor can’t always be trusted without a really strong understanding of the scene in question… and in a production workflow where shots get re-assigned regularly, that’s the beginning of a complex mess. Actually, most of the time re-assigning shots between animators is just asking for trouble on that front anyway. The only solution that gets around that is…. a pose matching feature.

I have enjoyed using an IK/FK pose matching switches on some rigs. Essentially allowing you to use the best method for different sections of a performance. The snag is the switch frame has to be maintained, and blending can get messy. It’s also a very complex tool to create and therefore viewed as a bit of a luxury that only high end projects tend to get. Using an auto-rig that implements it by default is my preferred way to go as suddenly it’s not a luxury and you get it consistently. You can also re-assign shots between animators and at least they have the option of switching methods. Although admittedly it’s an even more complex to┬ábake the switch across a range of frames.Anyway, it’s something that has to be thought about very carefully when you setup a character animation pipeline. Unfortunately most projects I’ve worked on have raced through this step and then suffer the debates further down the line while the animators struggle to work with the opposite method to their preference.

My short film, Devils Angels and Dating, was probably the smoothest experience I’ve ever had using Setup Machine to auto-rig the characters providing a pose match switch. I wish more studios would take a similar approach.

About the Author:
Michael Cawood is a multi-award winning British Animated Filmmaker with a broad skill set. Having worked in animation since 1994, he's created Films, Commercials, Games, Short Films and Animated Series.

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