[commieneko]

As an animator for 40 plus years, I can tell you that in-betweening is a very difficult job. The fact that it's often cheaply outsourced is more of a factor that the people paying for the animation simply don't care about the quality. The results are seldom good.

As to how much poor quality in-betweening hurts the performance to the audience is a complicated discussion. Animation that is _very_ bad can often be well accepted if other factors compensate (voice acting, design, direction, etc.)

A good in-betweener is not simply interpolating between the keys. For hand drawn animation at least, there's a lot more going on than that.

We'll leave out any discussion of breakdowns here. For one it's a difficult concept, much more difficult than 'tweening to explain. The other is that different animators will give different opinions on what a breakdown is or does.

I will say, though, I think that properly tagged breakdown drawings could significantly improve the performance of ai generated in-betweens.

Anyone who is seriously interested in the process should read the late, great Richard William's book, _The Animator's Survival Kit_. This is especially true for those who want to "augment" the process with machine learning. The book is very readable, even for non-artists. And he gets into the nitty gritty of what makes a good performance, and the mechanics behind it.

Edit: Another good resource, and relevant to 3D animation as well, is Raf Anzovin's _Just To Do Something Bad_ blog. He has many posts on what he calls "ephemeral rigging" that are absolutely fascinating. Be aware that the information is diffused through out the blog and not presented in a form for teaching. His opinions are fairly controversial in the field. But I think he is onto something. (https://www.justtodosomethingbad.com/)

[yosefk]

Post author here - would be very interesting to hear more of your thoughts on this! It's not easy to find a pro animator willing to consider the question given the current level reached by AI methods

[commieneko]

I would suggest reading the Williams book as a place to start. Thomas and Johnson's _The Illusion of Life_ is also a must. Thomas and Johnson were two of Disney's 9 old men. The Preston Blair book, simply called _Animation_ is good.

The thing about animation is that it is not about interpolation. It's about the spacing between drawings. The methods developed by animators were not at all mathematical, but something that they felt out by experimentation (trial and error).

The math that does enter into it are directly related to the frame rates. If animation had started in modern times, with frame rates of 30 fps or 60 fps, it would have been a very different animal. And much harder!

At 12 fpt or 24 fps you have a very limited range of "eases" that can be done. So while eases do figure into it, its the arcs, the articulation, and the perceived mass of the parts of the character that make it seem alive. Looking only at the contours and the in-betweens misses all the action.

An awareness of the graphic nature of the drawings, the stylizations of figures and faces are also critical. Cartooning is its own artform and it is tied directly to the way human brains make sense of what the eye sees. Getting more realistic often takes you further from your destination.

Storytelling is also a core part of good animation. Making a character seem to think and react, like it is alive can be done by a good animator. But you won't get there by imitating the real world directly. Rotoscoping has very limited use in good character animation and storytelling. It's all about abstracting out what the brain feels is important and what it expects. You can get away with murder if you caricature the right details.

When I've worked with training new animators, one of the points I stress is that it is articulation and the perceived mass of the character that really sells a performance. The best art style in the world is nearly useless if the viewer doesn't buy into the notion that they are watching a thinking person reacting with a physical body to events in an interactive world.

My feeling is that you will get further if you build articualated rigs and teach the ai to make it move. 2D or 3D. There is footage of tiny AI driven robots in a Google eperiement that are learning to play soccor. The ai is learning to make them move and solve problems (running around the soccar field and scoring goals.) Very natural looking behavior (animation!) develops almost automatically from that.

Trying to solve the problem by dealing with lines, contours, and interpolation seems very far away from the important parts of animtion.

Just my two cents worth.

Get a copy of the Williams book, it's on Amazon. Read his thoughts, he explains things much better, and more entertainingly, than I do. Sharpen up your pencil and start making some simple walks. Simple stick figures and tube people work just fine. And you may find that you enjoy the art form. Even if you don't become an animator yourself, the exercises will deepen your appreciation and understanding of the art form.

[yosefk]

I've read Williams' book, and I've studied animation and done some, though I wouldn't call myself an animator yet.

I hope to avoid building rigs because they're, well, rigs. Much nicer and more flexible to control things though drawing than a rig which has a bunch of limitations and then there are issues with hair/cloth/water/etc. What can be done without a rig is another question but the methods I reviewed in this post are not the most that can be done for sure.

[commieneko]

Rig can mean a lot of things. Hand drawn animators often use a rig, it’s just the rig is made of graphite lines on paper driven by a meat based neural network.

I'm not just being cute when I say that. The problems the AI in the examples was having have distinct analogs with the problems human animators have. Arcs are a problem, as is the notion that in-betweens are mostly about interpolation.

As I said, timing and articulation are at the heart of most kinds of animation. Even very stylized animation must be aware of this, if not being a slave to it. Imagination and expression are important, but first the audience has to _believe_.