Chapter 4 - Animation Basics

For this post, I will be sharing the notes I took from the Animation Basics chapter from the book: Principles of Three-Dimensional Computer Animation THIRD EDITION Modeling, Rendering and Animating with 3D Computer Graphics. The notes will be split into two posts.

4.1 Introduction

Animation is the production of a series of still images that once played back give the illusion of movement. The illusion produced by a physiological characteristics of our eyes known as persistence of vision. As animation is a sequence of still images or frames - each eye retains an afterimage of each frame for a brief moment and after that, the after images fills the minuscule gap broken the frame just before and after the next one.

In the early days of animation - particularly in Walt Disney Studios, they developed a technique to produce animation frames more efficiently - it was a case of drawing the most important frames of an animation sequence, these frames would be known as "Key"frames (key frames it is known as). Then a number of less experienced animators would draw in the actions that occur in between.

In 3D, the animator sets up the keyframes using any number of techniques, then the computer does the actions in between in each frame.

4.2 Keyframing

The simplest form of key frame animation is changing the values of this transformation matrix. When a three dimensional object is modeled digitally - it has a set of transformations known as a transformation matrix. The matrix has nine values to control (three in each):

- the overall placement of the model

- rotation

- scale of the model

You would define the first key within the timeline to where you want the animation to start as well as define where the transformation ends - you'd use the transformation matrix. The computer calculates the actions in between each frame.

Calculating the intermediate values is known as interpolating the values. The interpolated transformations values determine the immediate placement, size and scale of the object during the in between actions. This effectively making the computer a secondary animator. It's common practice to replay the animation over and over to make sure that all the transformations from frames A to B go as they should - this is done by using a motion preview that is available in certain software (although the name varies depending on your software).

4.3 Interpolations

In computer animation, interpolations are ways that animations vary the speed of transcations between each start and end of the transformation.

Linear Interpolation - the simplest form of interpolation, it gets the name (linear) from the fact put it into a graph, it's a straight line.

It's important to use more than one kind of interpolation, this can cause problems as it means that the changes within your animation are dramatic.

Using a Spline Interpolation you would get smooth transitions from your actions and also the key frames in the graph have a smooth curve. Spline Interpolation is not the only way to get smooth interpolation, messing about with the translation in Y for an object results in four different types of spline:

- Linear

- Cardinal

- B-Spline

- Bezier

Although have the same effect on key frames - they are all different in their own way. Beizier is the most commonly used.

4.4 Parameter-curve Editing

With keyframed animation - it's best to define the movement and timing of an object until it looks like it is suppose to look, then save it, the alternative approach to defining animations is using a graph.

The concept of the graph is that it is a graphical approach, changes made within the graph will appear in the animation. In parameter-curve editing systems - you can edit all curves in all the same ways you'd edit curves for a modelling process, So, adding a new point within the curve will immediately change the animation that is controlled by the curve.

Interpolations can be used for inbetween frames of two frames, even different kinds of interpolation can be used between two different frames. For Example, one kind of control points could be spline interpolation and another pair could contain another - this technique is particularly useful when you want an element of your animation to change for a certain amount of time but can remain unchanged for another.

Interpolations can also be used for inbetween frames of two frames, even different kinds of interpolation can be used between two different frames. For example, one kind of control points could be spline interpolation and another pair can be another - this technique is particularly useful when you want an element of your animation to change for a certain amount of time but can remain unchanged for another amount of time.

Stepped Interpolation - this keeps a parameter value constant through a range of frames then abruptly changes to the next value at the given frame. Since the value pops from one to the next instantaneously, it's sometimes referred to as an on/off interpolation. The effect this gives off is that the change happens almost instantly instead of gradually. This is perfect for someone to use if you're animating a light bulb going on and off.

Whatever kind of interpolation is being used, replaying it over and over to see if certain parts are going too fast or too slow - you'd length or shorten the sequence to make change to the speed. This kind of editing is known as scaling the animation. There are three ways of doing this:

- doing it through a menu window, where you'd type information such as the starting frame number to the sequence you want to scale the animation.

- using a dope sheer (which is explained further in the next post).

- using the parameter-curve editor to select a range of control points and then stretch them out to a fixed control point.

This sums up the first part of the information I received from this chapter, the rest will be posted in the next entry.