Introduction to Computer Graphics & Animation

by Alan Dorin
Happy Animator Animate - breathe life into, enliven through...
  • Movement

  • Character / Personality

  • Feeling / Emotion

  • Etc. etc. etc.

Movement is a powerful medium through which to convey a message to your audience.

Gertie the Dinosaur was (perhaps) the first real animated character. Gertie was created by cartoonist Winsor McCay in 1914. Unfortunately, due to copyright restrictions, Gertie cannot appear in person on this site. But you can read about her and check out some pictures elsewhere on the web.

Gertie Dinosaur

Nowadays, computers may be used to produce photo-realistic animated dinosaurs. Of course, if dinosaurs aren't to your liking, you can animate just about anything else too!

Animation is the process of creating images one at a time to be displayed rapidly in sequence...

Persistence of vision is the blending together by the eye/brain of rapidly displayed sequential images, giving the illusion of movement.

Three tasks for computer animation

Once the storyline, scenery, characters etc. have been developed, the production of computer images falls roughly into three major areas:
modelling Modelling - the process of specifying the geometric properties of an object.

Usually performed through a GUI allowing the user to select basic primitives (cones, spheres etc.) and modify their geometry by various means as well as decorate them with textures and connect them in hierarchies.

At this stage synthetic lights are also added to the model for the rendering process.
animating Animating - the process of specifying the time varying properties of a model.

Usually performed by a keyframing process where the model is posed at various times and the computer mathematically determines where the model ought to be positioned between these key frames.
rendering Rendering - the process of synthesizing images of a model.

Usually a computationally expensive process where imaginary light rays are bounced off the imaginary model at each time an image is required, and for each pixel in the image, to determined the colour visible to a viewer at that point in space.

Modelling - How is the model represented in the computer?

A model object may be stored within the computer by its:

Graphics Libraries

Non-Realtime Renderers

Animation - How does the model change over time?

A few simple transformations may be applied to the geometry of a model (such as Phillipa fish). These form the basis of much computer animation. To use these operations in the production of a computer-animated sequence, the computer stores a time line of the appropriate moments to apply an operation to a model and thereby change its characteristics.

Rendering - How do the pictures get to the screen?

There are a number of ways the geometry of a model may be drawn on the screen. Some of these are based around a set of routines stored in a graphics library. Graphics libraries often include procedures for rendering lines given their endpoints and surfaces given their vertices (see above).

Here are a few ways objects may be rendered to the screen.
Bounding box - objects are rendered as cubes which surround the more detailed geometry.

This method is mostly for rapid preview of models, it is not useful for much else.

Phillipa's bounding box
Wireframe - objects are rendered as if they were built out of wire or drinking straws attached at the vertices of the geometry.

This may often be performed with or without hidden-surface removal.

Phillipa's bounding box
Flat shaded - objects are rendered with facets as if they were made out of sheets of flat card. Each card is shaded in a uniform colour depending on the relative angle of its surface normal, light source and view point.

Phillipa wire frame
Gouraud shaded - objects are rendered with facets which are shaded non-uniformly in such a way as to help the surface of which they are a part look smooth.

Phillipa Gouraud
Phong shaded - as for Gouraud shading, only the algorithm for shading facets on the surface is superior and gives an excellent appearance of smoothness.

No amount of shading tricks in Gouraud or Phong shading can disguise a surface's polygonal/facetted nature along its silhouette.

Phillipa phong
Raytraced - surfaces which are supposed to be smooth are rendered as perfectly smooth. Since the surfaces are not rendered as facets, silhoutte edges are perfectly smooth also.

Raytracing works by bouncing rays of light from objects in the scene to the viewpoint. This can be a very time-consuming process, even for computers.

Raytracing allows renderings of reflective and transparent objects to be created. The more transparent or reflective objects there are in a scene, the slower the raytracing process will be.
Phillipa raytraced

Phillipa raytraced Here are a couple of close ups. Note the silhouette edge on Phillipa in each image.

How have these images been rendered?
Phillipa raytraced

Phillipa coloured too!

Looking for further information?

What you look at will depend on your aims. If you wish to start learning about 3d animation as a computer programmer, have a look at:

Whatever your aims, go and visit the library. There are many books there, and they're all available to you for no cost on top of the amount the government sees fit to charge you for your education!

You can also check out the web, including another more detailed lecture: introducing animation or one of the lectures listed for students of multimedia and the WWW.


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