History • Photography around since the 19th century • Realistic animation began in 1872 when Eadweard Muybridge asked to settle a bet about a flying horse Spring 2002 IT82: Multimedia 1 Spring 2002 IT82: Multimedia 2 © University of Stirling © University of Stirling History Early viewers • Muybridge did many studies of Many! human and animal motion, taking Includes: photographs against grid backgrounds • flipbook • He then displayed the photographs • zoetrope one after another, using a zoopraxiscope • The appearance of moving images was the first early animation – cartoon-like animation already existed Spring 2002 IT82: Multimedia 3 Spring 2002 IT82: Multimedia 4 © University of Stirling © University of Stirling Frame-by-Frame Animation How it works • Still images are rapidly displayed in sequence • If the positions of shapes on the images change, human perception is that the shapes move • Need 10 frames per second to give smooth flicker-free motion... • …but 50 needed in practice, where there are “blanks” in between images – cine projectors use one or more “blades” to cover the projector for a small period of time whilst the film advances • Note that the mains frequency is 52Hz ! • How do we produce the individual frames? Spring 2002 IT82: Multimedia 5 Spring 2002 IT82: Multimedia 6 © University of Stirling © University of Stirling 1 Bitmaps versus Vector • Same advantages/disadvantages of bitmaps and vector-based ways of representing moving images, only more so • The shapes/objects/figures need to be represented as such to meaningfully move them around • Again, same common practice: – Use vector-based file formats (or even metafiles) to store the animations – Export as a bitmapped version (typically compressed) Spring 2002 IT82: Multimedia 7 Spring 2002 IT82: Multimedia 8 © University of Stirling © University of Stirling Animation Creation Representation of Animation • Model Design – Uses modelling tool to produce the objects to be animated Various approaches: • Animation Design – Motion sequences planned • Keyframe animation – Lighting, action, interaction – 2D – Animation package uses all these to produce the animation – 3D script • Track-based animation • Rendering • Other approaches – Takes the script, and generates the images (i.e. vector to – Particle Systems bitmap conversion) – Hierarchical Systems • Post-production – Flock Systems The more these steps happen in one software package, the more convenient for the animator! Spring 2002 IT82: Multimedia 9 Spring 2002 IT82: Multimedia 10 © University of Stirling © University of Stirling Keyframe-based Animation Animation is done differently in 2D/3D based animation, but they have common properties: • Animator creates key frames, the software interpolates between them How should these frames be tweened? • Key frames hold all information about the state of the animation at that point in time • The creation of intermediate images between keyframes is known as in-betweening (or just tweening) • Sophisticated software allows the specification of different types of tweening Spring 2002 IT82: Multimedia 11 Spring 2002 IT82: Multimedia 12 © University of Stirling © University of Stirling 2 Morphing 2D • Control points are used in order to stretch (and • Animated image processing colour) the source image smoothly to the destination – uses morphing technique image • Cel animation Source Destination – flattened version of 3D – uses layers (cels) Richardson Section 3.3 Spring 2002 IT82: Multimedia 13 Spring 2002 IT82: Multimedia 14 © University of Stirling © University of Stirling Another Example • From F. Hofstetter, Multimedia Literacy, McGraw-Hill Spring 2002 IT82: Multimedia 15 Spring 2002 IT82: Multimedia 16 © University of Stirling © University of Stirling Cel Animation • The image is separated out into layers (cels) • Originally these cels would have been separate sheets of celluloid • Purpose of cels is to avoid unnecessary redrawing – e.g. when the background remains the same • Layers with characters on have control points Spring 2002 IT82: Multimedia 17 Spring 2002 IT82: Multimedia 18 © University of Stirling © University of Stirling 3 Bones • Control points are not sufficient to produce reasonable simulation of movement • Skeletons are used to keep different parts of the body together (both in biology and in animation) • Animation software allows the animator to define, connect, and move bones Spring 2002 IT82: Multimedia 19 Spring 2002 IT82: Multimedia 20 © University of Stirling © University of Stirling 3D • Morphing can be used - however, very much more computationally expensive to morph in 3D • The 3D equivalent of layers is to have scenes • Scenes contain a lot of state information, including – Background features – Lighting (number, light, position) – Camera position – Objects (size, shape, texture, position) • Each keyframe must record the state of all these objects for that keyframe Spring 2002 IT82: Multimedia 21 Spring 2002 IT82: Multimedia 22 © University of Stirling © University of Stirling Track-based Animation Particle Systems • These generalize key frame systems. • Not so much based on keyframes • With keyframes, each frame has the state information • More like a state machine for the entire scene. • These consist of a set (possibly varying in number) of • In track based systems each piece of state particles, and the rules of interaction between the information has its own “track”. particles • In a track, only values controlling interpolation are • Particles have their own state. This may typically be: specified at any one time – position • This reduces the amount of information to be – velocity recorded, and focuses the interpolation just on the – shape parameters pieces of state information that are important to the – colour animator. – transparency – lifetime Spring 2002 IT82: Multimedia 23 Spring 2002 IT82: Multimedia 24 © University of Stirling © University of Stirling 4 Particle Systems Other approaches • Hierarchical Animation – where objects relate to each other in a specific hierarchical • Each frame is generated from the previous one and way the interaction rules – e.g. the solar system, with moons revolving around planets • Useful for natural phenomena such as: revolving around the sun – smoke – rain • Flock Animation – fire – Like particles, but with rules like “follow the leader” – Saves effort, as the animator just needs to keyframe the leader, instead of all the members of the flock Spring 2002 IT82: Multimedia 25 Spring 2002 IT82: Multimedia 26 © University of Stirling © University of Stirling End of Lecture Spring 2002 IT82: Multimedia 27 © University of Stirling 5.