Technical Animation Pieces 1

// Here is the beginning of a blog series. This post will be updated after every technical animation class

 

Jan.25, 2017

from Walk Cycle to Motion Capture

– Stop Motion Animation

My classmates in class asked why it still exist. The reason is, there is too many factors that influence the reality, and we have only discovered ways to mimic it. We may achieve it in the future, or may not; but stop motion uses REAL PHYSICS. That is why I love stop motion animation. Actually, Laika is one of my favourite company.

What I love about stop motion animation:

  1. The Randomness in motion. Posing a real model with the artist’s hands feels different from using Maya. The frame-by-frame posing adds more style to the animation than setting key-frames. Think about flash animation verses hand-drawn animation and you will understand that different feelings.
  2. The Details in material and the lighting. Stop motion animation use real materials, and because the physics behind lighting is so complicated, every object respond uniquely. When lighting a scene, the materials and the lights always work together. The stop motion animations made by Laika are like exhibitions of the beauty of the materials, always make me feel intimate and satisfied.
  3. The Style itself. The animation in the movie Kubo and the Two Strings looks very fluent, but there’s still some parts (especially facial animation) that you can tell it is stop motion. Instead of feeling skeptical, I feel strongly into this kind of style. It is lovely and artistic.

And you can not deny, stop motion is the first 3D animation. In a way, computer animation referred to it when it first came out.

– Key Framing Animation and Motion Capture Animation

Different from my classmates’ opinion, I like the key framing animation better. And in animation feature, people seldom use motion capture. Motion capture can preserve the motion, but it has the limitation of reality. In animation, there is a balance between novelty and reality. If it looks too real, it is boring. If it is not real enough, it is not believable. Motion Capture creates realistic result, but too real. The philosophy of exaggerating in animation is lost in Motion Capture, and make it lose the style. Because of the fact that if you use motion capture, you will need to adjust the animation frame by frame, it is not ideal for animation features.

 

– Different Problems: Calculate Key Frame Animations, Transition Between Animation Clips and Motion Capture Displacement Curves

After the class I have some doubts about the difference between the three I mentioned above, so I did some research.

 

  • Keyframe Animation and Animation Curves

Here is a short description of maya’s graph editor.

https://knowledge.autodesk.com/support/maya-lt/learn-explore/caas/CloudHelp/cloudhelp/2015/ENU/MayaLT/files/Keyframe-Animation-Graph-Editor-overview-htm.html

Graph Editor in Maya

 

Keyframe animation is calculated based on interpolation.

 

  • Transition between 2 Animation Clips:

The actual problem is Animation Blending, It is used both on smooth transition between 2 animation clips and create new animations from existing ones. Also it can be used to combine multiple clips according to time-varying weights to get better result for motion capture.

The animations are represented with rotations. It is more complex than linear interpolation since it also involves complex problems like synchronization.

Use the example I found on stackoverflow:

Basically, if you have two animations clips A and B:

  • If A and B are completely different (blending jump and swimming), then chances are you will have strange/funny results;
  • If A and B are similar (two walking animation clips), then, you must first synchronize them to blend them when both left feet are on the ground for example.

The answer also mentioned a paper used a method called registration curves.

stackoverflow link : http://gamedev.stackexchange.com/questions/22402/animation-blending-basics

paper link: http://graphics.cs.wisc.edu/Papers/2003/KG03/regCurves.pdf

 

  • Displacement Curves on Motion Capture Results

This problem is more of a “spacetime constraint problem“. (A Hierarchical Approach to Interactive Motion Editing for Human-like Figures, 1999, http://dl.acm.org/citation.cfm?id=311539)

In this paper, it “combines a hierarchical curve fitting technique with a new inverse kinematics solver”. IK is calculated frame by frame to meet the constraints. The motion displacement of every joint at each constrained frame is interpolated and then the curve is smoothed.

 

  • Conclusion: All based on motion graph. Keyframe animations use linear interpolation as default. The two later problems both connect closely to the skeleton. The goal of transition is to get a right and smooth result, and adding displacement curves is more of a constraint problem.

 

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